Articulating diamond-surfaced spinal implants

ABSTRACT

Articulating diamond-surfaced spinal implants are disclosed. The implants use sintered polycrystalline articulation surfaces which are attached to spinal endplates and which are implanted to replace damaged spinal joints. The implants provide a long wearing and biocompatible articulation surface. Materials which may be used to make the spinal implants and manufacturing and finishing techniques for making the implants are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 10/229,907 filed on Aug. 28, 2002, now U.S. Pat. No. 7,494,507,which is continuation-in-part of U.S. patent application Ser. No.09/494,240 filed on Jan. 30, 2000, now U.S. Pat. No. 6,800,095, and U.S.patent application Ser. No. 10/229,907 filed on Aug. 28, 2002, now U.S.Pat. No. 7,494,507 claims priority to U.S. Provisional PatentApplication Ser. No. 60/315,545 filed on Aug. 28, 2001 and U.S.Provisional Patent Application Ser. No. 60/325,601 filed on Sep. 27,2001.

BACKGROUND

In the past, various spinal implants were known. Most prior art spinalimplants were adapted for fusion therapy, although there were somearticulating spinal implants as well.

SUMMARY

Various articulating diamond-surfaced spinal implants, materials formaking them, and methods for making them.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-1C depict sintering of a polycrystalline diamond compact.

FIGS. 1D & 2 depict formation of a diamond table on a substrate by aCVD, PVD or laser deposition method.

FIGS. 3-12 depict preparation of superhard materials for use in makingan articulating diamond-surfaced spinal implant component.

FIGS. 13-36 depict final preparation of superhard materials prior tosintering.

FIG. 37 depicts the anvils of a cubic press that may be used in makingsuperhard articulating diamond-surfaced spinal implant components.

FIGS. 38-50 depict machining and finishing superhard articulatingdiamond-surfaced spinal implant components.

FIGS. 51 and 52 depict a human spine.

FIGS. 53 to 112-3 depict various embodiments of spinal implants.

DETAILED DESCRIPTION

Various embodiments of the devices disclosed herein relate to superhardsurfaces for articulating diamond-surfaced spinal implants and materialsof various compositions, devices of various geometries, attachmentmechanisms, methods for making those superhard surfaces for articulatingdiamond-surfaced spinal implants and components, and products, whichinclude those superhard surfaces for articulating diamond-surfacedspinal implants and components. More specifically, some embodiments ofthe devices relate to diamond and sintered polycrystalline diamondsurfaces and articulating diamond-surfaced spinal implants that includediamond and polycrystalline diamond surfaces. Some embodiments of thedevices utilize a polycrystalline diamond compact (“PDC”) to provide avery strong, low friction, long-wearing surface in an articulatingdiamond-surfaced spinal implant. Any surface, including surfaces outsidethe field of articulating diamond-surfaced spinal implants, whichexperience wear and require strength and durability will benefit fromadvances made here.

There are several design objectives for articulating spinal implants.The implant should maintain height between adjacent vertebrae. It shouldproduce translational stability of the vertebrae. It should provide forintervertebral mobility. And the implant should reproduce disckinematics. Some embodiments of the spinal implants herein utilizecompound bearings and some use non-congruent bearings. One or more ofthe load bearing and articulation surfaces or contact surfaces of theimplant may utilize diamond for smooth and low-friction articulation.

The table below provides a comparison of sintered polycrystallinediamond (“PCD”) to some other materials.

TABLE 1 COMPARISON OF SINTERED PCD TO OTHER MATERIALS Thermal SpecificHardness Conductivity Material Gravity (Knoop) (W/m K) CTE (×10⁻⁶)Sintered 3.5-4.0 9000 900 1.50-4.8  Polycrystalline Diamond CompactCubic Boron Nitride 3.48 4500 800 1.0-4.0 Silicon Carbide 3.00 2500 844.7-5.3 Aluminum Oxide 3.50 2000 7.8-8.8 Tungsten Carbide 14.6 2200 1124-6 (10% Co) Cobalt Chrome 8.2 43 RC 16.9 Ti6Al4V 4.43 6.6-17.5 11Silicon Nitride 3.2 14.2 15-7  1.8-3.7

In view of the superior hardness of sintered PCD, it is expected thatsintered PCD will provide improved wear and durability characteristics.

Reference will now be made to the drawings in which the various elementsof the present devices will be discussed. Persons skilled in the designof articulating diamond-surfaced spinal implants and other surfaces willunderstand the application of the various embodiments of the devices andtheir principles to articulating diamond-surfaced spinal implants of alltypes, and components of articulating diamond-surfaced spinal implants,and devices other than those exemplified herein.

As discussed in greater detail below, the articulating diamond-surfacedspinal implant or articulating diamond-surfaced spinal implant componentmay use polycrystalline diamond compacts in order to form durable loadbearing and articulation surfaces. In a polycrystalline diamond compactthat includes a substrate, the diamond table may be chemically bondedand/or mechanically fixed to the substrate in a manufacturing processthat may use a combination of high pressure and high temperature to formthe sintered polycrystalline diamond. Alternatively, free-standingsintered polycrystalline diamond absent a substrate may be formed.Free-standing diamond (without a substrate) may also be referred to assolid diamond. The chemical bonds between diamond and a solvent-catalystmetal are established during the sintering process y combinations ofunsatisfied sp3 carbon bonds with unsatisfied substrate metal bonds.Where a substrate is used, the mechanical bond strength of the diamondtable to the substrate that results is a consequence of shape of thesubstrate and diamond table and differences in the physical propertiesof the substrate and the diamond table as well as the gradient interfacebetween the substrate and the diamond table. The resulting sinteredpolycrystalline diamond compact forms a durable articulatingdiamond-surfaced spinal implant or component.

The diamond table may be polished to a very smooth and glass-like finishto achieve a very low coefficient of friction. The high surface energyof sintered polycrystalline diamond compact causes it to work very wellas a load-bearing and articulation surface when a lubricating fluid ispresent. Its inherent nature allows it to perform very well when alubricant is absent as well.

While there is discussion herein concerning polycrystalline diamondcompacts, the following materials could be considered for forming anarticulating spinal implant or component: polycrystalline diamond,monocrystal diamond, natural diamond, diamond created by physical vapordeposition, diamond created by chemical vapor deposition, diamond likecarbon, carbonado, cubic boron nitride, hexagonal boron nitride, or acombination of these, cobalt, chromium, titanium, vanadium, stainlesssteel, niobium, aluminum, nickel, hafnium, silicon, tungsten,molybdenum, aluminum, zirconium, nitinol, cobalt chrome, cobalt chromemolybdenum, cobalt chrome tungsten, tungsten carbide, titanium carbide,tantalum carbide, zirconium carbide, hafnium carbide, Ti6/4, siliconcarbide, chrome carbide, vanadium carbide, yttria stabilized zirconia,magnesia stabilized zirconia, zirconia toughened alumina, titaniummolybdenum hafnium, alloys including one or more of the above metals,ceramics, quartz, garnet, sapphire, combinations of these materials,combinations of these and other materials, and other materials may alsobe used for a desired articulating diamond-surfaced spinal implant orcomponent.

Sintered Polycrystalline Diamond Compacts

One useful material for manufacturing articulating diamond-surfacedspinal implant surfaces, however, is a sintered polycrystalline diamondcompact due to its superior performance. Diamond has the greatesthardness and the lowest coefficient of friction of any currently knownmaterial. Sintered polycrystalline diamond compacts are chemicallyinert, are impervious to all solvents, and have the highest thermalconductivity at room temperature of any known material.

In some embodiments of the devices, a polycrystalline diamond compactprovides unique chemical bonding and mechanical grip between the diamondand the substrate material.

A method by which PDC may be manufactured is described later in thisdocument. Briefly, it involves sintering diamond crystals to each other,and to a substrate under high pressure and high temperature. FIGS. 1Aand 1B illustrate the physical and chemical processes involvedmanufacturing polycrystalline diamond compacts.

In FIG. 1A, a quantity of diamond feedstock 130 (such as diamond powderor crystals) is placed adjacent to a metal-containing substrate 110prior to sintering. In the region of the diamond feedstock 130,individual diamond crystals 131 may be seen, and between the individualdiamond crystals 131 there are interstitial spaces 132. If desired, aquantity of solvent-catalyst metal may be placed into the interstitialspaces 132. The substrate may also contain solvent-catalyst metal.

The substrate 110 may be a suitable pure metal or alloy, or a cementedcarbide containing a suitable metal or alloy as a cementing agent suchas cobalt-cemented tungsten carbide. The substrate may be a metal withhigh tensile strength. In a cobalt-chrome substrate of the devices, thecobalt-chrome alloy will serve as a solvent-catalyst metal for solvatingdiamond crystals during the sintering process.

The illustration shows the individual diamond crystals and thecontiguous metal crystals in the metal substrate. The interface 120between diamond powder and substrate material is a critical region wherebonding of the diamond table to the substrate must occur. In someembodiments of the devices, a boundary layer of a third materialdifferent than the diamond and the substrate is placed at the interface120. This interface boundary layer material, when present, may serveseveral functions including, but not limited to, enhancing the bond ofthe diamond table to the substrate, and mitigation of the residualstress field at the diamond-substrate interface.

Once diamond powder or crystals and substrate are assembled as shown inFIG. 1A, the assembly is subjected to high pressure and high temperatureas described later herein in order to cause bonding of diamond crystalsto diamond crystals and to the substrate. The resulting structure ofsintered polycrystalline diamond table bonded to a substrate is called apolycrystalline diamond compact (PDC). A compact, as the term is usedherein, is a composite structure of two different materials, such asdiamond crystals, and a substrate metal. The analogous structureincorporating cubic boron nitride crystals in the sintering processinstead of diamond crystals is called polycrystalline cubic boronnitride compact (PCBNC). Many of the processes described herein for thefabrication and finishing of PDC structures and parts work in a similarfashion for PCBNC. In some embodiments of the devices, PCBNC may besubstituted for PDC.

FIG. 1B depicts a polycrystalline diamond compact 101 after the highpressure and high temperature sintering of diamond feedstock to asubstrate. Within the PDC structure, there is an identifiable volume ofsubstrate 102, an identifiable volume of diamond table 103, and atransition zone 104 between diamond table and substrate containingdiamond crystals and substrate material. Crystalline grains of substratematerial 105 and sintered crystals of diamond 106 are depicted.

On casual examination, the finished compact of FIG. 1B will appear toconsist of a solid table of diamond 103 attached to the substrate 402with a discrete boundary. On very close examination, however, atransition zone 104 between diamond table 103 and substrate 102 can becharacterized. This zone represents a gradient interface between diamondtable and substrate with a gradual transition of ratios between diamondcontent and metal content. At the substrate side of the transition zone,there will be only a small percentage of diamond crystals and a highpercentage of substrate metal, and on the diamond table side, there willbe a high percentage of diamond crystals and a low percentage ofsubstrate metal. Because of this gradual transition of ratios ofpolycrystalline diamond to substrate metal in the transition zone, thediamond table and the substrate have a gradient interface.

In the transition zone or gradient transition zone where diamondcrystals and substrate metal are intermingled, chemical bonds are formedbetween the diamond and metal. From the transition zone 104 into thediamond table 103, the metal content diminishes and is limited tosolvent-catalyst metal that fills the three-dimensional vein-likestructure of interstitial voids, openings or asperities 107 within thesintered diamond table structure 103. The solvent-catalyst metal foundin the voids or openings 107 may have been swept up from the substrateduring sintering or may have been solvent-catalyst metal added to thediamond feedstock before sintering.

During the sintering process, there are three types of chemical bondsthat are created: diamond-to-diamond bonds, diamond-to-metal bonds, andmetal-to-metal bonds. In the diamond table, there are diamond-to-diamondbonds (sp3 carbon bonds) created when diamond particles partiallysolvate in the solvate-catalyst metal and then are bonded together. Inthe substrate and in the diamond table, there are metal-to-metal bondscreated by the high pressure and high temperature sintering process. Andin the gradient transition zone, diamond-to-metal bonds are createdbetween diamond and solvent-catalyst metal.

The combination of these various chemical bonds and the mechanical gripexerted by solvent-catalyst metal in the diamond table such as in theinterstitial spaces of the diamond structure diamond table provideextraordinarily high bond strength between the diamond table and thesubstrate. Interstitial spaces are present in the diamond structure andthose spaces typically are filled with solvent-catalyst metal, formingveins of solvent-catalyst metal within the polycrystalline diamondstructure. This bonding structure contributes to the extraordinaryfracture toughness of the compact, and the veins of metal within thediamond table act as energy sinks halting propagation of incipientcracks within the diamond structure. The transition zone and metal veinstructure provide the compact with a gradient of material propertiesbetween those of the diamond table and those of substrate material,further contributing to the extreme toughness of the compact. Thetransition zone can also be called an interface, a gradient transitionzone, a composition gradient zone, or a composition gradient, dependingon its characteristics. The transition zone distributesdiamond/substrate stress over the thickness of the zone, reducing zonehigh stress of a distinct linear interface. The subject residual stressis created as pressure and temperature are reduced at the conclusion ofthe high pressure/high temperature sintering process due to thedifference in pressure and thermal expansive properties of the diamondand substrate materials.

The diamond sintering process occurs under conditions of extremely highpressure and high temperature. According to the inventors' bestexperimental and theoretical understanding, the diamond sinteringprocess progresses through the following sequence of events. Atpressure, a cell containing feedstock of unbonded diamond powder orcrystals (diamond feedstock) and a substrate is heated to a temperatureabove the melting point of the substrate metal 110 and molten metalflows or sweeps into the interstitial voids 107 between the adjacentdiamond crystals 106. It is carried by the pressure gradient to fill thevoids as well as being pulled in by the surface energy or capillaryaction of the large surface area of the diamond crystals 106. As thetemperature continues to rise, carbon atoms from the surface of diamondcrystals dissolve into this interstitial molten metal, forming a carbonsolution.

At the proper threshold of temperature and pressure, diamond becomes thethermodynamically favored crystalline allotrope of carbon. As thesolution becomes super saturated with respect to Cd (carbon diamond),carbon from this solution begins to crystallize as diamond onto thesurfaces of diamond crystals bonding adjacent diamond crystals togetherwith diamond-diamond bonds into a sintered polycrystalline diamondstructure 106. The interstitial metal fills the remaining void spaceforming the vein-like lattice structure 107 within the diamond table bycapillary forces and pressure driving forces. Because of the crucialrole that the interstitial metal plays in forming a solution of carbonatoms and stabilizing these reactive atoms during the diamondcrystallization phase in which the polycrystalline diamond structure isformed, the metal is referred to as a solvent-catalyst metal.

FIG. 1 BB depicts a sintered polycrystalline diamond compact having bothsubstrate metal 180 and diamond 181, but in which there is a continuousgradient transition 182 from substrate metal to diamond. In such acompact, the gradient transition zone may be the entire compact, or aportion of the compact. The substrate side of the compact may containnearly pure metal for easy machining and attachment to other components,while the diamond side may be extremely hard, smooth and durable for usein a hostile work environment.

In some embodiments of the devices, a quantity of solvent-catalyst metalmay be combined with the diamond feedstock prior to sintering. This isfound to be useful when forming thick PCD tables, solid PDC structures,or when using multimodal fine diamond where there is little residualfree space within the diamond powder. In each of these cases, there maynot be sufficient ingress of solvent-catalyst metal via the sweepmechanism to adequately mediate the sintering process as asolvent-catalyst. The metal may be added by direct addition of powder,or by generation of metal powder in situ with an attritor mill or by thewell-known method of chemical reduction of metal salts deposited ondiamond crystals. Added metal may constitute any amount from less than1% by mass, to greater than 35%. This added metal may consist of thesame metal or alloy as is found in the substrate, or may be a differentmetal or alloy selected because of its material and mechanicalproperties. Example ratios of diamond feedstock to solvent-catalystmetal prior to sintering include mass ratios of 70:30, 85:15, 90:10, and95:15. The metal in the diamond feedstock may be added powder metal,metal added by an attritor method, vapor deposition or chemicalreduction of metal into powder.

When sintering diamond on a substrate with an interface boundary layer,it may be that no solvent-catalyst metal from the substrate is availableto sweep into the diamond table and participate in the sinteringprocess. In this case, the boundary layer material, if composed of asuitable material, metal or alloy that can function as asolvent-catalyst, may serve as the sweep material mediating the diamondsintering process. In other cases where the desired boundary materialcannot serve as a solvent-catalyst, a suitable amount ofsolvent-catalyst metal powder as described herein is added to thediamond crystal feed stock as described above. This assembly is thentaken through the sintering process. In the absence of a substrate metalsource, the solvent-catalyst metal for the diamond sintering processmust be supplied entirely from the added metal powder. The boundarymaterial may bond chemically to the substrate material, and bondschemically to the diamond table and/or the added solvent-catalyst metalin the diamond table. The remainder of the sintering and fabricationprocess may be the same as with the conventional solvent-catalyst sweepsintering and fabrication process.

For the sake of simplicity and clarity in this patent, the substrate,transition zone, and diamond table have been discussed as distinctlayers. However, it is important to realize that the finished sinteredobject may be a composite structure characterized by a continuousgradient transition from substrate material to diamond table rather thanas distinct layers with clear and discrete boundaries, hence the term“compact”.

In addition to the sintering processes described above, diamond partssuitable for use as articulating diamond-surfaced spinal implantscomponents may also be fabricated as solid or free-standingpolycrystalline diamond structures without a substrate. These may beformed by placing the diamond powder combined with a suitable amount ofadded solvent-catalyst metal powder as described above in a refractorymetal can (typically Ta, Nb, Zr, or Mo) with a shape approximating theshape of the final part desired. This assembly is then taken through thesintering process. However, in the absence of a substrate metal source,the solvent-catalyst metal for the diamond sintering process must besupplied entirely from the added metal powder. With suitable finishing,objects thus formed may be used as is, or bonded to metal or othersubstrates.

Sintering is a method of creating a diamond table with a strong anddurable constitution. Other methods of producing a diamond table thatmay or may not be bonded to a substrate are possible. At present, thesetypically are not as strong or durable as those fabricated with thesintering process. It is also possible to use these methods to formdiamond structures directly onto substrates suitable for use asarticulating diamond-surfaced spinal implants. A table ofpolycrystalline diamond either with or without a substrate may bemanufactured and later attached to an articulating diamond-surfacedspinal implant in a location such that it will form a surface. Theattachment could be performed with any suitable method, includingwelding, brazing, sintering, diffusion welding, diffusion bonding,inertial welding, adhesive bonding, or the use of fasteners such asscrews, bolts, or rivets. In the case of attaching a diamond tablewithout a substrate to another object, the use of such methods asbrazing, diffusion welding/bonding or inertia welding may be mostappropriate.

Although high pressure/high temperature sintering is a method forcreating a diamond surface, other methods for producing a volume ofdiamond may be employed as well. For example, either chemical vapordeposition (CVD), or physical vapor deposition (PVD) processes may beused. CVD produces a diamond layer by thermally cracking an organicmolecule and depositing carbon radicals on a substrate. PVD produces adiamond layer by electrically causing carbon radicals to be ejected froma source material and to deposit on a substrate where they build adiamond crystal structure.

The CVD and PVD processes have some advantages over sintering. Sinteringis performed in large, expensive presses at high pressure (such as 45-68kilobars) and at high temperatures (such as 1200 to 1500 degreesCelsius). It is difficult to achieve and maintain desired componentshape using a sintering process because of flow of high pressure mediumsused and possible deformation of substrate materials.

In contrast, CVD and PVD take place at atmospheric pressure or lower, sothere no need for a pressure medium and there is no deformation ofsubstrates.

Another disadvantage of sintering is that it is difficult to achievesome geometries in a sintered polycrystalline diamond compact. When CVDor PVD are used, however, the gas phase used for carbon radicaldeposition can completely conform to the shape of the object beingcoated, making it easy to achieve a desired non-planar shape.

Another potential disadvantage of sintering polycrystalline diamondcompacts is that the finished component will tend to have large residualstresses caused by differences in the coefficient of thermal expansionand modulus between the diamond and the substrate. While residualstresses can be used to improve strength of a part, they can also bedisadvantageous. When CVD or PVD is used, residual stresses can beminimized because CVD and PVD processes do not involve a significantpressure transition (such from 68 Kbar to atmospheric pressure in highpressure and high temperature sintering) during manufacturing.

Another potential disadvantage of sintering polycrystalline diamondcompacts is that few substrates have been found that are suitable forsintering. Tungsten carbide is a common choice for substrate materials.When CVD or PVD are used, however, synthetic diamond can be placed onmany substrates, including titanium, most carbides, silicon, molybdenumand others. This is because the temperature and pressure of the CVD andPVD coating processes are low enough that differences in coefficient ofthermal expansion and modulus between diamond and the substrate are notas critical as they are in a high temperature and high pressuresintering process.

A further difficulty in manufacturing sintered polycrystalline diamondcompacts is that as the size of the part to be manufactured increases,the size of the press must increase as well. Sintering of diamond willonly take place at certain pressures and temperatures, such as thosedescribed herein. In order to manufacture larger sinteredpolycrystalline diamond compacts, ram pressure of the press (tonnage)and size of tooling (such as dies and anvils) must be increased in orderto achieve the necessary pressure for sintering to take place. Butincreasing the size and capacity of a press is more difficult thansimply increasing the dimensions of its components. There may be apractical physical size constraints on press size due to themanufacturing process used to produce press tooling.

Tooling for a press is typically made from cemented tungsten carbide. Inorder to make tooling, the cemented tungsten carbide is sintered in avacuum furnace followed by pressing in a hot isostatic press (“HIP”)apparatus. Hipping must be performed in a manner that maintains uniformtemperature throughout the tungsten carbide in order to achieve uniformphysical qualities and quality. These requirements impose a practicallimit on the size tooling that can be produced for a press that isuseful for sintering polycrystalline diamond compacts. The limit on thesize tooling that can be produced also limits the size press that can beproduced.

CVD and PVD manufacturing apparatuses may be scaled up in size with fewlimitations, allowing them to produce polycrystalline diamond compactsof almost any desired size.

CVD and PVD processes are also advantageous because they permit precisecontrol of the thickness and uniformity of the diamond coating to beapplied to a substrate. Temperature is adjusted within the range of 500to 1000 degrees Celsius, and pressure is adjusted in a range of lessthan 1 atmosphere to achieve desired diamond coating thickness.

Another advantage of CVD and PVD processes is that they allow themanufacturing process to be monitored as it progresses. A CVD or PVDreactor can be opened before manufacture of a part is completed so thatthe thickness and quality of the diamond coating being applied to thepart may be determined. From the thickness of the diamond coating thathas already been applied, time to completion of manufacture can becalculated. Alternatively, if the coating is not of desired quality, themanufacturing processes may be aborted in order to save time and money.

In contrast, sintering of polycrystalline diamond compacts is performedas a batch process that cannot be interrupted, and progress of sinteringcannot be monitored. The pressing process must be run to completion andthe part may only be examined afterward.

CVD and PVD Diamond

CVD is performed in an apparatus called a reactor. A basic CVD reactorincludes four components. The first component of the reactor is one ormore gas inlets. Gas inlets may be chosen based on whether gases arepremixed before introduction to the chamber or whether the gases areallowed to mix for the first time in the chamber. The second componentof the reactor is one or more power sources for the generation ofthermal energy. A power source is needed to heat the gases in thechamber. A second power source may be used to heat the substratematerial uniformly in order to achieve a uniform coating of diamond onthe substrate. The third component of the reactor is a stage or platformon which a substrate is placed. The substrate will be coated withdiamond during the CVD process. Stages used include a fixed stage, atranslating stage, a rotating stage and a vibratory stage. Anappropriate stage must be chosen to achieved desired diamond coatingquality and uniformity. The fourth component of the reactor is an exitport for removing exhaust gas from the chamber. After gas has reactedwith the substrate, it must be removed from the chamber as quickly aspossible so that it does not participate in other reactions, which wouldbe deleterious to the diamond coating.

CVD reactors are classified according to the power source used. Thepower source is chosen to create the desired species necessary to carryout diamond thin film deposition. Some CVD reactor types includeplasma-assisted microwave, hot filament, electron beam, single, doubleor multiple laser beam, arc jet and DC discharge. These reactors differin the way they impart thermal energy to the gas species and in theirefficiency in breaking gases down to the species necessary fordeposition of diamond. It is possible to have an array of lasers toperform local heating inside a high pressure cell. Alternatively, anarray of optical fibers could be used to deliver light into the cell.

The basic process by which CVD reactors work is as follows. A substrateis placed into the reactor chamber. Reactants are introduced to thechamber via one or more gas inlets. For diamond CVD, methane (CH₄) andhydrogen (H₂) gases may be brought into the chamber in premixed form.Instead of methane, any carbon-bearing gas in which the carbon has sp3bonding may be used. Other gases may be added to the gas stream in orderto control quality of the diamond film, deposition temperature, gainstructure and growth rate. These include oxygen, carbon dioxide, argon,halogens and others.

The gas pressure in the chamber may be maintained at about 100 torr.Flow rates for the gases through the chamber may be about 10 standardcubic centimeters per minute for methane and about 100 standard cubiccentimeters per minute for hydrogen. The composition of the gas phase inthe chamber may be in the range of 90-99.5% hydrogen and 0.5-10%methane.

When the gases are introduced into the chamber, they are heated. Heatingmay be accomplished by many methods. In a plasma-assisted process, thegases are heated by passing them through a plasma. Otherwise, the gasesmay be passed over a series of wires such as those found in a hotfilament reactor.

Heating the methane and hydrogen will break them down into various freeradicals. Through a complicated mixture of reactions, carbon isdeposited on the substrate and joins with other carbon to formcrystalline diamond by sp3 bonding. The atomic hydrogen in the chamberreacts with and removes hydrogen atoms from methyl radicals attached tothe substrate surface in order to create molecular hydrogen, leaving aclear solid surface for further deposition of free radicals.

If the substrate surface promotes the formation of sp2 carbon bonds, orif the gas composition, flow rates, substrate temperature or othervariables are incorrect, then graphite rather than diamond will grow onthe substrate.

There are many similarities between CVD reactors and processes and PVDreactors and processes. PVD reactors differ from CVD reactors in the waythat they generate the deposition species and in the physicalcharacteristics of the deposition species. In a PVD reactor, a plate ofsource material is used as a thermal source, rather than having aseparate thermal source as in CVD reactors. A PVD reactor generateselectrical bias across a plate of source material in order to generateand eject carbon radicals from the source material. The reactor bombardsthe source material with high energy ions. When the high energy ionscollide with source material, they cause ejection of the desired carbonradicals from the source material. The carbon radicals are ejectedradially from the source material into the chamber. The carbon radicalsthen deposit themselves onto whatever is in their path, including thestage, the reactor itself, and the substrate.

Referring to FIG. 1D, a substrate 140 of appropriate material isdepicted having a deposition face 141 on which diamond may be depositedby a CVD or PVD process. FIG. 2 depicts the substrate 140 and thedeposition face 141 on which a volume of diamond 142 has been depositedby CVD or PVD processes. A small transition zone 143 is present in whichboth diamond and substrate are located. In comparison to FIG. 1B, it canbe seen that the CVD or PVD diamond deposited on a substrate lacks themore extensive gradient transition zone of sintered polycrystallinediamond compacts because there is no sweep of solvent-catalyst metalthrough the diamond table in a CVD or PVD process.

Both CVD and PVD processes achieve diamond deposition by line of sight.Means (such as vibration and rotation) are provided for exposing alldesired surfaces for diamond deposition. If a vibratory stage is to beused, the surface will vibrate up and down with the stage and therebypresent all surfaces to the free radical source.

There are several methods, which may be implemented in order to coatcylindrical objects with diamond using CVD or PVD processes. If a plasmaassisted microwave process is to be used to achieve diamond deposition,then the object to receive the diamond must be directly under the plasmain order to achieve the highest quality and most uniform coating ofdiamond. A rotating or translational stage may be used to present everyaspect of the surface to the plasma for diamond coating. As the stagerotates or translates, all portions of the surface may be broughtdirectly under the plasma for coating in such a way to achievesufficiently uniform coating.

If a hot filament CVD process is used, then the surface should be placedon a stationary stage. Wires or filaments (typically tungsten) arestrung over the stage so that their coverage includes the surface to becoated. The distance between the filaments and the surface and thedistance between the filaments themselves may be chosen to achieve auniform coating of diamond directly under the filaments.

Diamond surfaces can be manufactured by CVD and PVD process either bycoating a substrate with diamond or by creating a free standing volumeof diamond, which is later mounted for use. A free standing volume ofdiamond may be created by CVD and PVD processes in a two-step operation.First, a thick film of diamond is deposited on a suitable substrate,such as silicon, molybdenum, tungsten or others. Second, the diamondfilm is released from the substrate.

As desired, segments of diamond film may be cut away, such as by use ofa Q-switched YAG laser. Although diamond is transparent to a YAG laser,there is usually a sufficient amount of sp2 bonded carbon (as found ingraphite) to allow cutting to take place. If not, then a line may bedrawn on the diamond film using a carbon-based ink. The line should besufficient to permit cutting to start, and once started, cutting willproceed slowly.

After an appropriately-sized piece of diamond has been cut from adiamond film, it can be attached to a desired object in order to serveas a surface. For example, the diamond may be attached to a substrate bywelding, diffusion bonding, adhesion bonding, mechanical fixation orhigh pressure and high temperature bonding in a press.

Although CVD and PVD diamond on a substrate do not exhibit a gradienttransition zone that is found in sintered polycrystalline diamondcompacts, CVD and PVD process can be conducted in order to incorporatemetal into the diamond table. As mentioned elsewhere herein,incorporation of metal into the diamond table enhances adhesion of thediamond table to its substrate and can strengthen the polycrystallinediamond compact. Incorporation of diamond into the diamond table can beused to achieve a diamond table with a coefficient of thermal expansionand compressibility different from that of pure diamond, andconsequently increasing fracture toughness of the diamond table ascompared to pure diamond. Diamond has a low coefficient of thermalexpansion and a low compressibility compared to metals. Therefore thepresence of metal with diamond in the diamond table achieves a higherand more metal-like coefficient of thermal expansion and the averagecompressibility for the diamond table than for pure diamond.Consequently, residual stresses at the interface of the diamond tableand the substrate are reduced, and delamination of the diamond tablefrom the substrate is less likely.

A pure diamond crystal also has low fracture toughness. Therefore, inpure diamond, when a small crack is formed, the entire diamond componentfails catastrophically. In comparison, metals have a high fracturetoughness and can accommodate large cracks without catastrophic failure.Incorporation of metal into the diamond table achieves a greaterfracture toughness than pure diamond. In a diamond table havinginterstitial spaces and metal within those interstitial spaces, if acrack forms in the diamond and propagates to an interstitial spacecontaining metal, the crack will terminate at the metal and catastrophicfailure will be avoided. Because of this characteristic, a diamond tablewith metal in its interstitial spaces is able to sustain much higherforces and workloads without catastrophic failure compared to purediamond.

Diamond-diamond bonding tends to decrease as metal content in thediamond table increases. CVD and PVD processes can be conducted so thata transition zone is established. However, the surface can beessentially pure polycrystalline diamond for low wear properties.

Generally CVD and PVD diamond is formed without large interstitialspaces filled with metal. Consequently, most PVD and CVD diamond is morebrittle or has a lower fracture toughness than sintered polycrystallinediamond compacts. CVD and PVD diamond may also exhibit the maximumresidual stresses possible between the diamond table and the substrate.It is possible, however, to form CVD and PVD diamond film that has metalincorporated into it with either a uniform or a functionally gradientcomposition.

One method for incorporating metal into a CVD or PVD diamond film it touse two different source materials in order to simultaneously depositthe two materials on a substrate in a CVD of PVD diamond productionprocess. This method may be used regardless of whether diamond is beingproduced by CVD, PVD or a combination of the two.

Another method for incorporating metal into a CVD diamond film chemicalvapor infiltration. This process would first create a porous layer ofmaterial, and then fill the pores by chemical vapor infiltration. Theporous layer thickness should be approximately equal to the desiredthickness for either the uniform or gradient layer. The size anddistribution of the pores can be sued to control ultimate composition ofthe layer. Deposition in vapor infiltration occurs first at theinterface between the porous layer and the substrate. As depositioncontinues, the interface along which the material is deposited movesoutward from the substrate to fill pores in the porous layer. As thegrowth interface moves outward, the deposition temperature along theinterface is maintained by moving the sample relative to a heater or bymoving the heater relative to the growth interface. It is imperativethat the porous region between the outside of the sample and the growthinterface be maintained at a temperature that does not promotedeposition of material (either the pore-filling material or undesiredreaction products). Deposition in this region would close the poresprematurely and prevent infiltration and deposition of the desiredmaterial in inner pores. The result would be a substrate with openporosity and poor physical properties.

Laser Deposition of Diamond

Another alternative manufacturing process that may be used to producesurfaces and components of the devices involves use of energy beams,such as laser energy, to vaporize constituents in a substrate andredeposit those constituents on the substrate in a new form, such as inthe form of a diamond coating. As an example, a metal, polymeric orother substrate may be obtained or produced containing carbon, carbidesor other desired constituent elements. Appropriate energy, such as laserenergy, may be directed at the substrate to cause constituent elementsto move from within the substrate to the surface of the substrateadjacent the area of application of energy to the substrate. Continuedapplication of energy to the concentrated constituent elements on thesurface of the substrate can be used to cause vaporization of some ofthose constituent elements. The vaporized constituents may then bereacted with another element to change the properties and structure ofthe vaporized constituent elements.

Next, the vaporized and reacted constituent elements (which may bediamond) may be diffused into the surface of the substrate. A separatefabricated coating may be produced on the surface of the substratehaving the same or a different chemical composition than that of thevaporized and reacted constituent elements. Alternatively, some of thechanged constituent elements which were diffused into the substrate maybe vaporized and reacted again and deposited as a coating on the. Bythis process and variations of it, appropriate coatings such as diamond,cubic boron nitride, diamond like carbon, B₄C, SiC, TiC, TiN, TiB, cCN,Cr₃C₂, and Si₃N₄ may be formed on a substrate.

In other manufacturing environments, high temperature laser application,electroplating, sputtering, energetic laser excited plasma deposition orother methods may be used to place a volume of diamond, diamond-likematerial, a hard material or a superhard material in a location in whichwill serve as a surface.

In light of the disclosure herein, those of ordinary skill in the artwill comprehend the apparatuses, materials and process conditionsnecessary for the formation and use of high quality diamond on asubstrate using any of the manufacturing methods described herein inorder to create a diamond surface.

Material Property Considerations

There is a particular problem posed by the manufacture of a non-planardiamond surface. The non-planar component design requires that pressuresbe applied radially in making the part. During the high pressuresintering process, described in detail below, all displacements must bealong a radian emanating from the center of the part that will beproduced in order to achieve the desired non-planar geometry. To achievethis in high temperature/high pressure pressing, an isostatic pressurefield must be created. During the manufacture of such non-planar parts,if there is any deviatoric stress component, it will result indistortion of the part and may render the manufactured part useless.

Special considerations that must be taken into account in makingnon-planar polycrystalline diamond compacts are discussed below.

Modulus

Most polycrystalline diamond compacts include both a diamond table and asubstrate. The material properties of the diamond and the substrate maybe compatible, but the high pressure and high temperature sinteringprocess in the formation of a polycrystalline diamond compact may resultin a component with excessively high residual stresses. For example, fora polycrystalline diamond compact using tungsten carbide as thesubstrate, the sintered diamond has a Young's modulus of approximately120 million p.s.i., and cobalt cemented tungsten carbide has a modulusof approximately 90 million p.s.i. Modulus refers to the slope of thecurve of the stress plotted against the stress for a material. Modulusindicates the stiffness of the material. Bulk modulus refers to theratio of isostatic strain to isostatic stress, or the unit volumereduction of a material versus the applied pressure or stress.

Because diamond and most substrate materials have such a high modulus, avery small stress or displacement of the polycrystalline diamond compactcan induce very large stresses. If the stresses exceed the yieldstrength of either the diamond or the substrate, the component willfail. The strongest polycrystalline diamond compact is not necessarilystress free. In a sintered polycrystalline diamond compact with optimaldistribution of residual stress, more energy is required to induce afracture than in a stress free component. Thus, the difference inmodulus between the substrate and the diamond must be noted and used todesign a component that will have the best strength for its applicationwith sufficient abrasion resistance and fracture toughness.

Coefficient of Thermal Expansion (CTE)

The extent to which diamond and its substrate differ in how they deformrelative to changes in temperature also affects their mechanicalcompatibility. Coefficient of thermal expansion (“CTE”) is a measure ofthe unit change of a dimension with unit change in temperature or thepropensity of a material to expand under heat or to contract whencooled. As a material experiences a phase change, calculations based onCTE in the initial phase will not be applicable. It is notable that whencompacts of materials with different CTE's and moduluses are used, theywill stress differently at the same stress.

Polycrystalline diamond has a coefficient of thermal expansion (as aboveand hereafter referred to as “CTE” on the order of 2-4 micro inches perinch (10⁻⁶ inches) of material per degree (in/in° C.). In contrast,carbide has a CTE on the order of 6-8 in/in° C. Although these valuesappear to be close numerically, the influence of the high moduluscreates very high residual stress fields when a temperature gradient ofa few hundred degrees is imposed upon the combination of substrate anddiamond. The difference in coefficient of thermal expansion is less of aproblem in simple planar polycrystalline diamond compacts than in themanufacture of non-planar or complex shapes. When a non-planarpolycrystalline diamond compact is manufactured, differences in the CTEbetween the diamond and the substrate can cause high residual stresswith subsequent cracking and failure of the diamond table, the substrateor both at any time during or after high pressure/high temperaturesintering.

Dilatoric and Deviatoric Stresses

The diamond and substrate assembly will experience a reduction of freevolume during the sintering process. The sintering process, described indetail below, involves subjecting the substrate and diamond assembly topressure ordinarily in the range of about 40 to about 68 kilobar. Thepressure will cause volume reduction of the substrate. Some geometricaldistortion of the diamond and/or the substrate may also occur. Thestress that causes geometrical distortion is called deviatoric stress,and the stress that causes a change in volume is called dilatoricstress. In an isostatic system, the deviatoric stresses sum to zero andonly the dilatoric stress component remains. Failure to consider all ofthese stress factors in designing and sintering a polycrystallinediamond component with complex geometry (such as concave and convexnon-planar polycrystalline diamond compacts) will likely result infailure of the process.

Free Volume Reduction of Diamond Feedstock

As a consequence of the physical nature of the feedstock diamond, largeamounts of free volume are present unless special preparation of thefeedstock is undertaken prior to sintering. It is necessary to eliminateas much of the free volume in the diamond as possible, and if the freevolume present in the diamond feedstock is too great, then sintering maynot occur. It is also possible to eliminate the free volume duringsintering if a press with sufficient ram displacement is employed. Isimportant to maintain a desired uniform geometry of the diamond andsubstrate during any process which reduces free volume in the feedstock,or a distorted or faulty component may result.

Selection of Solvent-Catalyst Metal

Formation of synthetic diamond in a high temperature and high pressurepress without the use of a solvent-catalyst metal is not a viable methodat this time, although it may become viable in the future. Asolvent-catalyst metal is at this time required to achieve desiredcrystal formation in synthetic diamond. The solvent-catalyst metal firstsolvates carbon preferentially from the sharp contact points of thediamond feedstock crystals. It then recrystallizes the carbon as diamondin the interstices of the diamond matrix with diamond-diamond bondingsufficient to achieve a solid with 95 to 97% of theoretical density withsolvent metal 5-3% by volume. That solid distributed over the substratesurface is referred to herein as a polycrystalline diamond table. Thesolvent-catalyst metal also enhances the formation of chemical bondswith substrate atoms.

A method for adding the solvent-catalyst metal to diamond feedstock isby causing it to sweep from the substrate that contains solvent-catalystmetal during high pressure and high temperature sintering. Powderedsolvent-catalyst metal may also be added to the diamond feedstock beforesintering, particularly if thicker diamond tables are desired. Anattritor method may also be used to add the solvent-catalyst metal todiamond feedstock before sintering. If too much or too littlesolvent-catalyst metal is used, then the resulting part may lack thedesired mechanical properties, so it is important to select an amount ofsolvent-catalyst metal and a method for adding it to diamond feedstockthat is appropriate for the particular part to be manufactured.

Diamond Feedstock Particle Size and Distribution

The durability of the finished diamond product is integrally linked tothe size of the feedstock diamond and also to the particle distribution.Selection of the proper size(s) of diamond feedstock and particledistribution depends upon the service requirement of the specimen andalso its working environment. The durability of polycrystalline diamondis enhanced if smaller diamond feedstock crystals are used and a highlydiamond-diamond bonded diamond table is achieved.

Although polycrystalline diamond may be made from single modal diamondfeedstock, use of multi-modal feedstock increases both impact strengthand wear resistance. The use of a combination of large crystal sizes andsmall crystal sizes of diamond feedstock together provides a part withhigh impact strength and wear resistance, in part because theinterstitial spaces between the large diamond crystals may be filledwith small diamond crystals. During sintering, the small crystals willsolvate and reprecipitate in a manner that binds all of the diamondcrystals into a strong and tightly bonded compact.

Diamond Feedstock Loading Methodology

Contamination of the diamond feedstock before or during loading willcause failure of the sintering process. Great care must be taken toensure the cleanliness of diamond feedstock and any addedsolvent-catalyst metal or binder before sintering.

In order to prepare for sintering, clean diamond feedstock, substrate,and container components are prepared for loading. The diamond feedstockand the substrate are placed into a refractory metal container called a“can” which will seal its contents from outside contamination. Thediamond feedstock and the substrate will remain in the can whileundergoing high pressure and high temperature sintering in order to forma polycrystalline diamond compact. The can may be sealed by electronbeam welding at high temperature and in a vacuum.

Enough diamond aggregate (powder or grit) is loaded to account forlinear shrinkage during high pressure and high temperature sintering.The method used for loading diamond feedstock into a can for sinteringaffects the general shape and tolerances of the final part. Inparticular, the packing density of the feedstock diamond throughout thecan should be as uniform as possible in order to produce a good qualitysintered polycrystalline diamond compact structure. In loading, bridgingof diamond can be avoided by staged addition and packing.

The degree of uniformity in the density of the feedstock material afterloading will affect geometry of the polycrystalline diamond compact.Loading of the feedstock diamond in a dry form versus loading diamondcombined with a binder and the subsequent process applied for theremoval of the binder will also affect the characteristics of thefinished polycrystalline diamond compact. In order to properlypre-compact diamond for sintering, the pre-compaction pressures shouldbe applied under isostatic conditions.

Selection of Substrate Material

The unique material properties of diamond and its relative differencesin modulus and CTE compared to most potential substrate materialsdiamond make selection of an appropriate polycrystalline diamondsubstrate a formidable task. A great disparity in material propertiesbetween the diamond and the substrate creates challenges successfulmanufacture of a polycrystalline diamond component with the neededstrength and durability. Even very hard substrates appear to be softcompared to polycrystalline diamond. The substrate and the diamond mustbe able to withstand not only the pressure and temperature of sintering,but must be able to return to room temperature and atmospheric pressurewithout delaminating, cracking or otherwise failing.

Selection of substrate material also requires consideration of theintended application for the part, impact resistance and strengthsrequired, and the amount of solvent-catalyst metal that will beincorporated into the diamond table during sintering. Substratematerials must be selected with material properties that are compatiblewith those of the diamond table to be formed.

Substrate Geometry

Further, it is important to consider whether to use a substrate whichhas a smooth surface or a surface with topographical features. Substratesurfaces may be formed with a variety of topographical features so thatthe diamond table is fixed to the substrate with both a chemical bondand a mechanical grip. Use of topographical features on the substrateprovides a greater surface area for chemical bonds and with themechanical grip provided by the topographical features, can result in astronger and more durable component.

Example Materials and Manufacturing Steps

The inventors have discovered and determined materials and manufacturingprocesses for constructing polycrystalline diamond compacts for use inan articulating diamond-surfaced spinal implant. It is also possible tomanufacture the invented surfaces by methods and using materials otherthan those listed below.

The steps described below, such as selection of substrate material andgeometry, selection of diamond feedstock, loading and sintering methods,will affect each other, so although they are listed as separate stepsthat must be taken to manufacture a polycrystalline diamond compact, nostep is completely independent of the others, and all steps must bestandardized to ensure success of the manufacturing process.

Select Substrate and/or Solvent-Catalyst Metal

In order to manufacture any polycrystalline diamond component, anappropriate substrate should be selected. For the manufacture of apolycrystalline diamond component to be used in an articulatingdiamond-surfaced spinal implant, various substrates may be used asdesired.

TABLE 2 SOME SUBSTRATES FOR ARTICULATING DIAMOND-SURFACED SPINAL IMPLANTAPPLICATIONS Substrate Alloy Name Remarks Titanium Ti6/4 (TiAlVa) A thintantalum barrier may ASTM F-1313 (TiNbZr) be placed on the titanium ASTMF-620 substrate before loading diamond ASTM F-1580 feedstock. TiMbHfNitinol (TiNi + other) Cobalt chrome ASTM F-799 Contains cobalt,chromium and molybdenum. Wrought product Cobalt chrome ASTM F-90Contains cobalt, chromium, tungsten and nickel. Cobalt chrome ASTM F-75Contains cobalt, chromium and molybdenum. Cast product. Cobalt chromeASTM F-562 Contains cobalt, chromium, molybdenum and nickel. Cobaltchrome ASTM F-563 Contains cobalt, chromium, molybdenum, tungsten, ironand nickel. Tantalum ASTM F-560 (unalloyed) refractory metal. Platinumvarious Niobium ASTM F-67 (unalloyed) refractory metal. Maganese VariousMay include Cr, Ni, Mg, molybdenum. Cobalt cemented tungsten WC Commonlyused in carbide synthetic diamond production Cobalt chrome cemented CoCrcemented WC tungsten carbide Cobalt chrome cemented CoCr cemented CrCchrome carbide Cobalt chrome cemented CoCr cemented SiC silicon carbideFused silicon carbide SiC Cobalt chrome CoCrMo A thin tungsten ormolybdenum tungsten/cobalt layer may be placed on the substrate beforeloading diamond feedstock. Stainless steel Various

The CoCr used as a substrate or solvent-catalyst metal may be CoCrMo orCoCrW or another suitable CoCr. Alternatively, an Fe-based alloy, aNi-based alloy (such as Co—Cr—W—Ni) or another alloy may be used. Co andNi alloys tend to provide a corrosion-resistant component. The precedingsubstrates and solvent-catalyst metals are examples only. In addition tothese substrates, other materials may be appropriate for use assubstrates for construction of articulating diamond-surfaced spinalimplant s and other surfaces.

When titanium is used as the substrate, sometimes place a thin tantalumbarrier layer is placed on the titanium substrate. The tantalum barrierprevents mixing of the titanium alloys with cobalt alloys used in thediamond feedstock. If the titanium alloys and the cobalt alloys mix, itpossible that a detrimentally low melting point eutectic inter-metalliccompound will be formed during the high pressure and high temperaturesintering process. The tantalum barrier bonds to both the titanium andcobalt alloys, and to the polycrystalline diamond that contains cobaltsolvent-catalyst metals. Thus, a polycrystalline diamond compact madeusing a titanium substrate with a tantalum barrier layer and diamondfeedstock that has cobalt solvent-catalyst metals can be very strong andwell formed. Alternatively, the titanium substrate may be provided withan alpha case oxide coating (an oxidation layer) forming a barrier whichprevents formation of a eutectic metal.

If a cobalt chrome molybdenum substrate is used, a thin tungsten layeror a thin tungsten and cobalt layer can be placed on the substratebefore loading of the diamond feedstock in order to control formation ofchrome carbide (CrC) during sintering.

In addition to those listed, other appropriate substrates may be usedfor forming polycrystalline diamond compact surfaces. Further, it ispossible within the scope of the devices to form a diamond surface foruse without a substrate. It is also possible to form a surface from anyof the superhard materials and other materials listed herein, in whichcase a substrate may not be needed. Additionally, if it is desired touse a type of diamond or carbon other than polycrystalline diamond,substrate selection may differ. For example, if a diamond surface is tobe created by use of chemical vapor deposition or physical vapordeposition, then use of a substrate appropriate for those manufacturingenvironments and for the compositions used will be necessary.

Determination of Substrate Geometry

A substrate geometry appropriate for the compact to be manufactured andappropriate for the materials being used should be selected. In order tomanufacture a non-planar diamond surface, it is necessary to select asubstrate geometry that will facilitate the manufacture of those parts.In order to ensure proper diamond formation and avoid compactdistortion, forces acting on the diamond and the substrate duringsintering must be strictly radial. Therefore the substrate geometry atthe contact surface with diamond feedstock for manufacturing a complexsurface in some instances may be generally non-planar.

As mentioned previously, there is a great disparity in the materialcharacteristics of synthetic diamond and most available substratematerials. In particular, modulus and CTE are of concern. But whenapplied in combination with each other, some substrates can form astable and strong polycrystalline diamond compact. The table below listsphysical properties of some substrate materials.

TABLE 3 MATERIAL PROPERTIES OF SOME EXAMPLE SUBSTRATES Substrate LModulus CTE Ti 6/4 16.5 million psi 5.4 CoCrMo 35.5 million psi 16.9CoCrW 35.3 million psi 16.3

Use of either titanium or cobalt chrome substrates alone for themanufacture of non-planar polycrystalline diamond compacts may result incracking of the diamond table or separation of the substrate from thediamond table. In particular, it appears that titanium's dominantproperty during high pressure and high temperature sintering iscompressibility while cobalt chrome's dominant property during sinteringis CTE. In some embodiments of the devices, a substrate of two or morelayers may be used in order to achieve dimensional stability during andafter manufacturing.

In various embodiments of the devices, a single layer substrate may beutilized. In other embodiments of the devices, a two-layer substrate maybe utilized, as discussed. Depending on the properties of the componentsbeing used, however, it may be desired to utilize a substrate thatincludes three, four or more layers. Such multi-layer substrates areintended to be comprehended within the scope of the devices.

Substrate Surface Topography

Depending on the application, it may be advantageous to includesubstrate surface topographical features on a substrate that is to beformed into a polycrystalline diamond compact. Regardless whether aone-piece, a two-piece of a multi-piece substrate is used, it may bedesirable to modify the surface of the substrate or providetopographical features on the substrate in order to increase the totalsurface area of diamond to enhance substrate to diamond contact and toprovide a mechanical grip of the diamond table.

The placement of topographical features on a substrate serves to modifythe substrate surface geometry or contours from what the substratesurface geometry or contours would be if formed as a simple planar ornon-planar figure. Substrate surface topographical features may includeone or more different types of topographical features which result inprotruding, indented or contoured features that serve to increasesurface, mechanically interlock the diamond table to the substrate,prevent crack formation, or prevent crack propagation.

Substrate surface topographical features or substrate surfacemodifications serve a variety of useful functions. Use of substratetopographical features increases total substrate surface area of contactbetween the substrate and the diamond table. This increased surface areaof contact between diamond table and substrate results in a greatertotal number of chemical bonds between diamond table and substrate thanif the substrate surface topographical features were absent, thusachieving a stronger polycrystalline diamond compact.

Substrate surface topographical features also serve to create amechanical interlock between the substrate and the diamond table. Themechanical interlock is achieved by the nature of the substratetopographical features and also enhances strength of the polycrystallinediamond compact.

Substrate surface topographical features may also be used to distributethe residual stress field of the polycrystalline diamond compact over alarger surface area and over a larger volume of diamond and substratematerial. This greater distribution can be used to keep stresses belowthe threshold for crack initiation and/or crack propagation at thediamond table/substrate interface, within the diamond itself and withinthe substrate itself.

Substrate surface topographical features increase the depth of thegradient interface or transition zone between diamond table andsubstrate, in order to distribute the residual stress field through alonger segment of the composite compact structure and to achieve astronger part.

Substrate surface modifications can be used to created a sinteredpolycrystalline diamond compact that has residual stresses that fortifythe strength of the diamond layer and yield a more robustpolycrystalline diamond compact with greater resistance to breakage thanif no surface topographical features were used. This is because in orderto break the diamond layer, it is necessary to first overcome theresidual stresses in the part and then overcome the strength of thediamond table.

Substrate surface topographical features redistribute forces received bythe diamond table. Substrate surface topographical features cause aforce transmitted through the diamond layer to be re-transmitted fromsingle force vector along multiple force vectors. This redistribution offorces traveling to the substrate avoids conditions that would deformthe substrate material at a more rapid rate than the diamond table, assuch differences in deformation can cause cracking and failure of thediamond table.

Substrate surface topographical features may be used to mitigate theintensity of the stress field between the diamond and the substrate inorder to achieve a stronger part.

Substrate surface topographical features may be used to distribute theresidual stress field throughout the polycrystalline diamond compactstructure in order to reduce the stress per unit volume of structure.

Substrate surface topographical features may be used to mechanicallyinterlock the diamond table to the substrate by causing the substrate tocompress over an edge of the diamond table during manufacturing.Dovetailed, heminon-planar and lentate modifications act to provideforce vectors that tend to compress and enhance the interface of diamondtable and substrate during cooling as the substrate dilitates radially.

Substrate surface topographical features may also be used to achieve amanufacturable form. As mentioned herein, differences in coefficient ofthermal expansion and modulus between diamond and the chosen substratemay result in failure of the polycrystalline diamond compact duringmanufacturing. For certain parts, the stronger interface betweensubstrate and diamond table that may be achieved when substratetopographical features are used can achieve a polycrystalline diamondcompact that can be successfully manufactured. But if a similar part ofthe same dimensions is to be made using a substrate with a simplesubstrate surface rather than specialized substrate surfacetopographical features, the diamond table may crack or separate from thesubstrate due to differences in coefficient of thermal expansion ormodulus of the diamond and the substrate.

Examples of useful substrate surface topographical features includewaves, grooves, ridges, other longitudinal surface features (any ofwhich may be arranged longitudinally, lattitudinally, crossing eachother at a desired angle, in random patterns, and in geometricpatterns), three dimensional textures, non-planar segment depressions,non-planar segment protrusions, triangular depressions, triangularprotrusions, arcuate depressions, arcuate protrusions, partiallynon-planar depressions, partially non-planar protrusions, cylindricaldepressions, cylindrical protrusions, rectangular depressions,rectangular protrusions, depressions of n-sided polygonal shapes where nis an integer, protrusions of n-sided polygonal shapes, a waffle patternof ridges, a waffle iron pattern of protruding structures, dimples,nipples, protrusions, ribs, fenestrations, grooves, troughs or ridgesthat have a cross-sectional shape that is rounded, triangular, arcuate,square, polygonal, curved, or otherwise, or other shapes. Machining,pressing, extrusion, punching, injection molding and other manufacturingtechniques for creating such forms may be used to achieve desiredsubstrate topography. Although for illustration purposes, some sharpcorners are depicted on substrate topography or other structures in thedrawings, in practice it is expected that all corners will have a smallradius to achieve a component with superior durability.

Although many substrate topographies have been depicted in convexnon-planar substrates, those surface topographies may be applied toconvex non-planar substrate surfaces, other non-planar substratesurfaces, and flat substrate surfaces. Substrate surface topographieswhich are variations or modifications of those shown, and othersubstrate topographies which increase component strength or durabilitymay also be used.

Diamond Feedstock Selection

It is anticipated that typically the diamond particles used will be inthe range of less than 1 micron to more than 100 microns. In someembodiments of the devices, however, diamond particles as small as 1nanometer may be used. Smaller diamond particles are used for smoothersurfaces. Commonly, diamond particle sizes will be in the range of 0.5to 2.0 microns or 0.1 to 10 microns.

An example diamond feedstock is shown in the table below.

TABLE 4 EXAMPLE BIMODAL DIAMOND FEEDSTOCK Material Amount 4 to 8 microndiamond about 90% 0.5 to 1.0 micron diamond about 9% Titaniumcarbonitride powder about 1%

This formulation mixes some smaller and some larger diamond crystals sothat during sintering, the small crystals may dissolve and thenrecrystallize in order to form a lattice structure with the largerdiamond crystals. Titanium carbonitride powder may optionally beincluded in the diamond feedstock in order to prevent excessive diamondgrain growth during sintering in order to produce a finished productthat has smaller diamond crystals.

Another diamond feedstock example is provided in the table below.

TABLE 5 EXAMPLE TRIIMODAL DIAMOND FEEDSTOCK Material Amount Size xdiamond crystals about 90% Size 0.1x diamond crystals about 9% Size0.01x diamond crystals about 1%

The trimodal diamond feedstock described above can be used with anysuitable diamond feedstock having a first size or diameter “x”, a secondsize 0.1x and a third size 0.01x. This ratio of diamond crystals allowspacking of the feedstock to about 89% theoretical density, closing mostinterstitial spaces and providing the densest diamond table in thefinished polycrystalline diamond compact.

Another diamond feedstock example is provided in the table below.

TABLE 6 EXAMPLE TRIIMODAL DIAMOND FEEDSTOCK Material Amount Size xdiamond crystals about 88-92% Size 0.1x diamond crystals about 8-12%Size 0.01x diamond crystals about 0.8-1.2%

Another diamond feedstock example is provided in the table below.

TABLE 7 EXAMPLE TRIIMODAL DIAMOND FEEDSTOCK Material Amount Size xdiamond crystals about 85-95% Size 0.1x diamond crystals about 5-15%Size 0.01x diamond crystals about 0.5-1.5%

Another diamond feedstock example is provided in the table below.

TABLE 8 EXAMPLE TRIIMODAL DIAMOND FEEDSTOCK Material Amount Size xdiamond crystals about 80-90% Size 0.1x diamond crystals about 10-20%Size 0.01x diamond crystals about 0-2%

In some embodiments of the devices, the diamond feedstock used will bediamond powder having a greatest dimension of about 100 nanometers orless. In some embodiments of the devices some solvent-catalyst metal isincluded with the diamond feedstock to aid in the sintering process,although in many applications there will be a significantsolvent-catalyst metal sweep from the substrate during sintering aswell.

Solvent Metal Selection

It has already been mentioned that solvent metal will sweep from thesubstrate through the diamond feedstock during sintering in order tosolvate some diamond crystals so that they may later recrystallize andform a diamond-diamond bonded lattice network that characterizespolycrystalline diamond. It is possible to include some solvent-catalystmetal in the diamond feedstock only when required to supplement thesweep of solvent-catalyst metal from the substrate.

Traditionally, cobalt, nickel and iron have been used as solvent metalsfor making polycrystalline diamond. Platinum and other materials couldalso be used for a binder.

CoCr may be used as a solvent-catalyst metal for sintering PCD toachieve a more wear resistant PDC. Infiltrating diamond particles withCobalt (Co) metal produces standard polycrystalline diamond compact. Asthe cobalt infiltrates the diamond, carbon is dissolved (mainly from thesmaller diamond grains) and reprecipitates onto the larger diamondgrains causing the grains to grow together. This is known as liquidphase sintering. The remaining pore spaces between the diamond grainsare filled with cobalt metal.

In this example, the alloy Cobalt Chrome (CoCr) may be used as thesolvent metal which acts similarly to Co metal. However, it differs inthat the CoCr reacts with some of the dissolved carbon resulting in theprecipitation of CoCr carbides. These carbides, like most carbides, areharder (abrasion resistant) than cobalt metal and results in a more wearor abrasion resistant PDC.

Other metals can be added to Co to form metal carbides as precipitateswithin the pore spaces between the diamond grains. These metals includethe following, but not limited to, Ti, W, Mo, V, Ta, Nb, Zr, Si, andcombinations thereof.

It is important not just to add the solvent metal to diamond feedstock,but also to include solvent metal in an appropriate proportion and tomix it evenly with the feedstock. The use of about 86% diamond feedstockand 15% solvent metal by mass (weight) has provided good result, otheruseful ratios of diamond feedstock to solvent metal may include 5:95,10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 65:35, 75:25, 80:20, 90:10,95:5, 97:3, 98:2, 99:1, 99.5:0.5, 99.7:0.3, 99.8:0.2, 99.9:0.1 andothers.

In order to mix the diamond feedstock with solvent-catalyst metal, firstthe amounts of feedstock and solvent metal to be mixed may be placedtogether in a mixing bowl, such as a mixing bowl made of the desiredsolvent-catalyst metal. Then the combination of feedstock and solventmetal may be mixed at an appropriate speed (such as 200 rpm) with drymethanol and attritor balls for an appropriate time period, such as 30minutes. The attritor balls, the mixing fixture and the mixing bowl maybe made from the solvent-catalyst metal. The methanol may then bedecanted and the diamond feedstock separated from the attritor balls.The feedstock may then be dried and cleaned by firing in a molecularhydrogen furnace at about 1000 degrees Celsius for about 1 hour. Thefeedstock is then ready for loading and sintering. Alternatively, it maybe stored in conditions which will preserve its cleanliness. Appropriatefurnaces which may be used for firing also include hydrogen plasmafurnaces and vacuum furnaces.

Loading Diamond Feedstock

Referring to FIG. 3, an apparatus for carrying out a loading techniqueis depicted. The apparatus includes a spinning rod 301 with alongitudinal axis 302, the spinning rod being capable of spinning aboutits longitudinal axis. The spinning rod 701 has an end 303 matched tothe size and shape of the part to be manufactured. For example, if thepart to be manufactured is non-planar, the spinning rod end 303 may beheminon-planar.

A compression ring 304 is provided with a bore 305 through which thespinning rod 301 may project. A die 306 or can is provided with a cavity307 also matched to the size and shape of the part to be made.

In order to load diamond feedstock, the spinning rod is placed into adrill chuck and the spinning rod is aligned with the center point of thedie. The depth to which the spinning rod stops in relation to the cavityof the die is controlled with a set screw and monitored with a dialindicator.

The die is charged with a known amount of diamond feedstock material.The spinning rod is then spun about its longitudinal axis and loweredinto the die cavity to a predetermined depth. The spinning rod contactsand rearranges the diamond feedstock during this operation. Then thespinning of the spinning rod is stopped and the spinning rod is lockedin place.

The compression ring is then lowered around the outside of the spinningrod to a point where the compression ring contacts diamond feedstock inthe cavity of the die. The part of the compression ring that contactsthe diamond is annular. The compression ring is tamped up and down tocompact the diamond. This type of compaction is used to distributediamond material throughout the cavity to the same density and may bedone in stages to prevent bridging. Packing the diamond with thecompaction ring causes the density of the diamond around the equator ofthe sample caused to be very uniform and the same as that of the polarregion in the cavity. In this configuration, the diamond sinters in atruly non-planar fashion and the resulting part maintains its sphericityto close tolerances.

Controlling Large Volumes of Powder Feedstocks, Such as Diamond

The following information provides further instruction on control andpre-processing of diamond feedstock before sintering. PolycrystallineDiamond Compact (PDC) and Polycrystalline Cubic Boron Nitride (PCBN)powders reduce in volume during the sintering process. The amount ofshrinkage experienced is dependent on a number of factors such as:

The amount of metal mixed with the diamond.

The loading density of the powders.

The bulk density of diamond metal mix.

The volume of powder loaded.

Particle size distribution (PSD) of the powders.

In most PDC and CBN sintering applications, the volume of powder used issmall enough that shrinkage is easily managed, as shown in FIG. 3A-1. InFIG. 3A, we can see a can 3A-54 in which can halves 3A-53 contain asubstrate 3A-52 and a diamond table 3A-51. However, when sintering largevolumes of diamond powders in spherical configurations, shrinkage isgreat enough to cause buckling of the containment cans 3A-66 as shown inFIG. 3A-2 and the cross section of FIG. 3A-3. The diamond has sintered3A-75 but the can has buckles 3A-77 and wrinkles 3A-78, resulting in anon-uniform and damaged part. The following method is an improvedloading, pre-compression, densification, and refractory can sealingmethod for spherical and non-planar parts loaded with large volumes ofdiamond and/or metal powders. The processing steps are described below.

Referring to FIG. 3A-4 and its cross section at FIG. 3A-5, PDC or PCBNpowders 3A-911 are loaded against a substrate 3A-99 and into arefractory metal containment can 3A-910 having a seal 3A-912. Extrapowder may be loaded normal to the seam in the cans to accommodateshrinkage.

Referring to FIG. 3A-6, a can assembly 3A-913 is placed into compactionfixture 3A-1014, which may be a cylindrical holder or slide 3A-1015 withtwo hemispherical punches 3A-1016 and 3A-1017. The fixture is designedto support the containment cans and allow the cans to slip at the seamduring the pressing operation.

Referring to FIG. 3A-7-1, relationship of the can half skins 3A-910 withthe junction 3A-912 and the punch 3A-1016 is seen.

Referring to FIG. 3A-7, fixture 3A-1014 with can 3A-913 is placed into apress 3A-1218 and the upper and lower punches compress the can assembly.The containment can halves slip past each other preventing bucklingwhile the powdered feedstock is compressed.

Referring to FIG. 3A-8, the upper punch is retracted and a crimping dieis attached to the cylinder.

Referring to FIGS. 3A-9 and 3A-9-1, the lower punch is raised drivingexcess can material into the hemispherical portion of the crimping diefolding the excess around the upper can.

Referring to FIG. 3A-10, the lower punch is raised expelling the canassembly from the cylinder.

Referring to FIG. 3A-11, the can assembly emerges from pressingoperation spherical with high loading density. The part can then besintered in a cubic or other press without buckling or breaking thecontainment cans.

Binding Diamond Feedstock Generally

Another method which may be employed to maintain a uniform density ofthe feedstock diamond is the use of a binder. A binder is added to thecorrect volume of feedstock diamond, and then the combination is pressedinto a can. Some binders which might be used include polyvinyl butyryl,polymethyl methacrylate, polyvinyl formol, polyvinyl chloride acetate,polyethylene, ethyl cellulose, methylabietate, paraffin wax,polypropylene carbonate and polyethyl methacrylate.

In one embodiment of the devices, the process of binding diamondfeedstock includes four steps. First, a binder solution is prepared. Abinder solution may be prepared by adding about 5 to 25% plasticizer topellets of poly(propylene carbonate), and dissolving this mixture insolvent such as 2-butanone to make about a 20% solution by weight.

Plasticizers that may be used include nonaqueous binders generally,glycol, dibutyl phthalate, benzyl butyl phthalate, alkyl benzylphthalate, diethylhexyl phthalate, diisoecyl phthalate, diisononylphthalate, dimethyl phthalate, dipropylene glycol dibenzoate, mixedglycols dibenzoate, 2-ethylhexyl diphenyl dibenzoate, mixed glycolsdibenzoate, 2-ethylhexyl diphenyl phosphate, isodecyl diphenylphosphate, isodecyl diphenl phosphate, tricrestyl phosphate, tributoxyethyl phosphate, dihexyl adipate, triisooctyl trimellitate, dioctylphthalate, epoxidized linseed oil, epoxidized soybean oil, acetyltriethyl citrate, propylene carbonate, various phthalate esters, butylstearate, glycerin, polyalkyl glycol derivatives, diethyl oxalate,paraffin wax and triethylene glycol. Other appropriate plasticizers maybe used as well.

Solvents that may be used include 2-butanone, methylene chloride,chloroform, 1,2-dichloroethane, trichlorethylene, methyl acetate, ethylacetate, vinyl acetate, propylene carbonate, n-propyl acetate,acetonitrile, dimethylformamide, propionitrile, n-methyl-2-pyrrolidene,glacial acetic acid, dimethyl sulfoxide, acetone, methyl ethyl ketone,cyclohexanone, oxysolve 80a, caprotactone, butyrolactone,tetrahydrofuran, 1,4 dioxane, propylene oxide, cellosolve acetate,2-methoxy ethyl ether, benzene, styrene, xylene, ethanol, methanol,toluene, cyclohexane, chlorinated hydrocarbons, esters, ketones, ethers,ethyl benzene and various hydrocarbons. Other appropriate solvents maybe used as well.

Second, diamond is mixed with the binder solution. Diamond may be addedto the binder solution to achieve about a 2-25% binder solution (thepercentage is calculated without regard to the 2-butanone).

Third, the mixture of diamond and binder solution is dried. This may beaccomplished by placing the diamond and binder solution mixture in avacuum oven for about 24 hours at about 50 degrees Celsius in order todrive out all of the solvent 2-butanone. Fourth, the diamond and bindermay be pressed into shape. When the diamond and binder is removed fromthe oven, it will be in a clump that may be broken into pieces which arethen pressed into the desired shape with a compaction press. A pressingspindle of the desired geometry may be contacted with the bound diamondto form it into a desired shape. When the diamond and binder have beenpressed, the spindle is retracted. The final density of diamond andbinder after pressing may be at least about 2.6 grams per cubiccentimeter.

If a volatile binder is used, it should be removed from the shapeddiamond prior to sintering. The shaped diamond is placed into a furnaceand the binding agent is either gasified or pyrolized for a sufficientlength of time such that there is no binder remaining. Polycrystallinediamond compact quality is reduced by foreign contamination of thediamond or substrate, and great care must be taken to ensure thatcontaminants and binder are removed during the furnace cycle. Ramp upand the time and temperature combination are critical for effectivepyrolization of the binder. For the binder example given above, thedebinding process that may be used to remove the binder is as follows.Reviewing FIG. 4 while reading this description may be helpful.

First, the shaped diamond and binder are heated to from ambienttemperature to about 500 degrees Celsius. The temperature may beincreased by about 2 degrees Celsius per minute until about 500 degreesCelsius is reached. Second, the temperature of the bound and shapeddiamond is maintained at about 500 degrees Celsius for about 2 hours.Third, the temperature of the diamond is increased again. Thetemperature may be increased from about 500 degrees Celsius by about 4degrees per minute until a temperature of about 950 degrees Celsius isreached. Fourth, the diamond is maintained at about 950 degrees Celsiusfor about 6 hours. Fifth, the diamond is then permitted to return toambient temperature at a temperature decrease of about 2 degrees perminute.

In some embodiments of the devices, it may be desirable to preform bounddiamond feedstock by an appropriate process, such as injection molding.The diamond feedstock may include diamond crystals of one or more sizes,solvent-catalyst metal, and other ingredients to control diamondrecrystallization and solvent-catalyst metal distribution. Handling thediamond feedstock is not difficult when the desired final curvature ofthe part is flat, convex dome or conical. However, when the desiredfinal curvature of the part has complex contours, such as illustratedherein, providing uniform thickness and accuracy of contours of thepolycrystalline diamond compact is more difficult when using powderdiamond feedstock. In such cases it may be desirable to perform thediamond feedstock before sintering.

If it is desired to perform diamond feedstock prior to loading into acan for sintering, rather than placing powder diamond feedstock into thecan, the steps described herein and variations of them may be followed.First, as already described, a suitable binder is added to the diamondfeedstock. Optionally, powdered solvent-catalyst metal and othercomponents may be added to the feedstock as well. The binder willtypically be a polymer chosen for certain characteristics, such asmelting point, solubility in various solvents, and CTE. One or morepolymers may be included in the binder. The binder may also include anelastomer and/or solvents as desired in order to achieve desiredbinding, fluid flow and injection molding characteristics. The workingvolume of the binder to be added to a feedstock may be equal to orslightly more than the measured volume of empty space in a quantity oflightly compressed powder. Since binders typically consist of materialssuch as organic polymers with relatively high CTE's, the working volumeshould be calculated for the injection molding temperatures expected.The binder and feedstock should be mixed thoroughly to assure uniformityof composition. When heated, the binder and feedstock will havesufficient fluid character to flow in high pressure injection molding.The heated feedstock and binder mixture is then injected under pressureinto molds of desired shape. The molded part then cools in the molduntil set, and the mold can then be opened and the part removed.Depending on the final polycrystalline diamond compact geometry desired,one or more molded diamond feedstock component can be created and placedinto a can for polycrystalline diamond compact sintering. Further, useof this method permits diamond feedstock to be molded into a desiredform and then stored for long periods of time prior to use in thesintering process, thereby simplifying manufacturing and resulting inmore efficient production.

As desired, the binder may be removed from the injection molded diamondfeedstock form. A variety of methods are available to achieve this. Forexample, by simple vacuum or hydrogen furnace treatment, the binder maybe removed from the diamond feedstock form. In such a method, the formwould be brought up to a desired temperature in a vacuum or in a verylow pressure hydrogen (reducing) environment. The binder will thenvolatilize with increasing temperature and will be removed from theform. The form may then be removed from the furnace. When hydrogen isused, it helps to maintain extremely clean and chemically activesurfaces on the diamond crystals of the diamond feedstock form.

An alternative method for removing the binder from the form involvesutilizing two or polymer (such as polyethylene) binders with differentmolecular weights. After initial injection molding, the diamondfeedstock form is placed in a solvent bath which removes the lowermolecular weight polymer, leaving the higher molecular weight polymer tomaintain the shape of the diamond feedstock form. Then the diamondfeedstock form is placed in a furnace for vacuum or very low pressurehydrogen treatment for removal of the higher molecular weight polymer.

Partial or complete binder removal from the diamond feedstock form maybe performed prior to assembly of the form in a pressure assembly forpolycrystalline diamond compact sintering. Alternatively, the pressureassembly including the diamond feedstock form may be placed into afurnace for vacuum or very low pressure hydrogen furnace treatment andbinder removal.

Dilute Binder

In some embodiments, dilute binder may be added to PCD, PCBN or ceramicpowders to hold form. This technique may be used to provide an improvedmethod of forming Polycrystalline Diamond Compact (PDC), PolycrystallineCubic Boron Nitride (PCBN), ceramic, or cermet powders into layers ofvarious geometries. A PDC, PCBN, ceramic or cermet powder may be mixedwith a temporary organic binder. This mixture may be mixed and cast orcalendared into a sheet (tape) of the desired thickness. The sheet maybe dried to remove water or organic solvents. The dried tape may be thencut into shapes needed to conform to the geometry of a correspondingsubstrate. The tape/substrate assembly may be then heated in a vacuumfurnace to drive off the binder material. The temperature may be thenraised to a level where the ceramic or cermet powder fuses to itselfand/or to the substrate, thereby producing a uniform continuous ceramicor cermet coating bonded to the substrate.

Referring to FIG. 5, a die 55 with a cup/can in it 54 and diamondfeedstock against it 52 are depicted. A punch 53 is used to form thediamond feedstock into a desired shape. Binder liquid 51 is not added tothe powder until after the diamond, PCBN, ceramic or cermet powder 52 isin the desired geometry. Dry powder 52 is spin formed using a rotatingformed punch 53 in a refectory containment can 54 supported in a holdingdie 55. In another method shown in FIG. 6, feedstock powder 62 is addedto a mold 66. A punch forms the feedstock to shape. A vibrator 67 may beused help the powder 62 take on the shape of the mold 66. After thepowder feedstock is in the desired geometry, a dilute solution of anorganic binder with a solvent is allowed to percolate through the powdergranules.

As shown in FIGS. 7 and 8, one powder layer 88 can be loaded, and aftera few minutes, when the binder is cured sufficiently at roomtemperature, another layer 89 can be loaded on top of the first layer88. This method is particularly useful in producing PDC or CBN withmultiple layers of varying powder particle size and metal content. Theprocess can be repeated to produce as many layers as desired. FIG. 7shows a section view of a spherical, multi-layered powder load using afirst layer 88, second layer 89, third layer 810, and final layer 811.The binder content should be kept to minimum to produce good loadingdensity and to limit the amount of gas produced during the binderremoval phase to reduce the tendency of the containment cans beingdisplaced from a build up of internal pressure.

Once all of the powder layers are loaded the binder may be burned-out ina vacuum oven at a vacuum of about 200 Militorrs or less and at the timeand desired temperature profile, such as that shown in FIG. 9. Anacceptable binder is 0.5 to 5% propylene carbonate in methyl ethylkeytone. An example binder burn out cycle that may be used to removebinder is as follows:

Time (minutes) Temperature (degrees Centigrade) 0 21 4 100 8 250 60 250140 800 170 800 290 21Gradients

Diamond feedstock may be selected and loaded in order to createdifferent types of gradients in the diamond table. These include aninterface gradient diamond table, an incremental gradient diamond table,and a continuous gradient diamond table.

If a single type or mix of diamond feedstock is loaded adjacent asubstrate, as discussed elsewhere herein, sweep of solvent-catalystmetal through the diamond will create an interface gradient in thegradient transition zone of the diamond table.

An incremental gradient diamond table may be created by loading diamondfeedstocks of differing characteristics (diamond particle size, diamondparticle distribution, metal content, etc.) in different strata orlayers before sintering. For example, a substrate is selected, and afirst diamond feedstock containing 60% solvent-catalyst metal by weightis loaded in a first strata adjacent the substrate. Then a seconddiamond feedstock containing 40% solvent-catalyst metal by weight isloaded in a second strata adjacent the first strata. Optionally,additional strata of diamond feedstock may be used. For example, a thirdstrata of diamond feedstock containing 20% solvent-catalyst metal byweight may be loaded adjacent the second strata.

A continuous gradient diamond table may be created by loading diamondfeedstock in a manner that one or more of its characteristicscontinuously vary from one depth in the diamond table to another. Forexample, diamond particle size may vary from large near a substrate (inorder to create large interstitial spaces in the diamond forsolvent-catalyst metal to sweep into) to small near the diamond surfacein order to create a part that is strongly bonded to the substrate butthat has a very low friction surface.

The diamond feedstocks of the different strata may be of the same ordifferent diamond particle size and distribution. Solvent-catalyst metalmay be included in the diamond feedstock of the different strata inweight percentages of from about 0% to more than about 80%. In someembodiments, diamond feedstock will be loaded with no solvent-catalystmetal in it, relying on sweep of solvent-catalyst metal from thesubstrate to achieve sintering. Use of a plurality of diamond feedstockstrata, the strata having different diamond particle size anddistribution, different solvent-catalyst metal by weight, or both,allows a diamond table to be made that has different physicalcharacteristics at the interface with the substrate than at the surface.This allows a polycrystalline diamond compact to be manufactured whichhas a diamond table very firmly bonded to its substrate.

Bisquing Processes to Hold Shapes

If desired, a bisquing process may be used to hold shapes for subsequentprocessing of polycrystalline diamond compacts, polycrystalline cubicboron nitride, and ceramic or cermet products. This involves an interimprocessing step in High Temperature High Pressure (HTHP) sintering ofPolycrystalline Diamond Compact (PDC), Polycrystalline Boron Nitride(PCBN), ceramic, or cermet powders called “bisquing.” Bisquing mayprovide the following enhancements to the processing of the aboveproducts:

Pre-sintered shapes can be controlled that are at a certain density andsize.

Product consistency is improved dramatically.

Shapes can be handled easily in the bisque form.

In layered constructs, bisquing keeps the different layers fromcontaminating each other.

Bisquing different components or layers separately increase theseparation of work elements increasing production efficiency andquality.

Bisquing molds are often easier to handle and manage prior to finalassembly that the smaller final product forms.

Bisquing molds or containers can be fabricated from any high temperaturematerial that has a melting point higher than the highest melting pointof any mix component to be bisque. Bisque mold/container materials thatwork well are Graphite, Quartz, Solid Hexagonal Boron Nitride (HBN), andceramics. Some refractory type metals (High temperature stainlesssteels, Nb, W, Ta, Mo, etc) work well is some applications wherebisquing temperatures are lower and sticking of the bisque powder mix isnot a problem. Molds or containers can be shaped by pressing, forming,or machining, and are preferably polished at the interface between thebisque material and the mold/container itself. Some mold/containermaterials glazing and/or firing prior to use.

FIG. 10 shows an embodiment 1006 for making a cylinder with a concaverelief or trough using the bisquing process. Pre-mixed powders of PDC,PCBN, ceramic, or cermet materials 1001 which contain enough metal toundergo solid phase sintering are loaded into the bisquing molds orcontainers 1002 and 1004. A release agent may be required between themold/container to ensure that the final bisque form can be removedfollowing furnace firing. Some release agents that may be used are HBN,Graphite, Mica, and Diamond Powder. A bisque mold/container lid with anintegral support form 1005 is placed over the loaded powder material toensure that the material holds form during the sintering process. Thebisque mold/container assembly is then placed in a hydrogen atmospherefurnace, or alternately, in a vacuum furnace which is drawn to a vacuumranging from 200 to 0 Militorrs. The load is then heated within a rangeof 0.6 to 0.8 of the melting temperature of the largest volume mixmetal. A typical furnace cycle is shown in FIG. 12. Once the furnacecycle is completed and the mold/container is cooled, the hardened bisqueformed powders can be removed for further HPHT processing. A bisque formof feedstock 1003 is the net product.

FIG. 11 shows fabrication 1110 of a bisque form for a full hemisphericalpart 1109 that has multiple powder layers 1107 a and 1107 b. Pre-mixedpowders of PDC, PCBN, ceramic, or cermet materials which contain enoughmetal to undergo solid phase sintering are loaded into the bisquingmolds or containers. A release agent may be required between themold/container to ensure that the final bisque form can be removedfollowing furnace firing. The bisque mold/container assembly may thenplaced in a vacuum furnace which is drawn to a vacuum ranging from 200to 0 Militorrs. The load is then heated within a range of 0.6 to 0.8 ofthe melting temperature of the largest volume mix metal. Once thefurnace cycle is completed and the mold/container is cooled, thehardened bisque 1109 formed powders can be removed for further HPHTprocessing. An example of a bisque binder burn-out cycle that may beused to remove the unwanted materials before sintering is as follows:

Time (hours) Temperature (degrees Centigrade) 0 21 0.25 21 5.19 800 6.19800 10.19 21Reduction of Free Volume in Diamond Feedstock

As mentioned earlier, it may be desirable to remove free volume in thediamond feedstock before sintering is attempted. This may be a usefulprocedure especially when producing non-planar concave and convex parts.If a press with sufficient anvil travel is used for high pressure andhigh temperature sintering, however, this step may not be necessary.Free volume in the diamond feedstock may in some instances be reduced sothat the resulting diamond feedstock is at least about 95% theoreticaldensity and sometimes closer to about 97% of theoretical density.

Referring to FIGS. 13 and 14 a, an assembly used for precompressingdiamond to eliminate free volume is depicted. In the drawing, thediamond feedstock is intended to be used to make a convex non-planarpolycrystalline diamond part. The assembly may be adapted forprecompressing diamond feedstock for making polycrystalline diamondcompacts of other complex shapes.

The assembly depicted includes a cube 1301 of a pressure transfermedium. A cube is made from pyrophillite or other appropriate pressuretransfer material such as a synthetic pressure medium and is intended toundergo pressure from a cubic press with anvils simultaneously pressingthe six faces of the cube. A cylindrical cell rather than a cube wouldbe used if a belt press were utilized for this step.

The cube 801 has a cylindrical cavity 1302 or passage through it. Thecenter of the cavity 1302 will receive a non-planar refractory metal can1310 loaded with diamond feedstock 806 that is to be precompressed. Thediamond feedstock 1306 may have a substrate with it.

The can 1310 consists of two heminon-planar can halves 1310 a and 1310b, one of which overlaps the other to form a slight lip 1312. The canmay be an appropriate refractory metal such as niobium, tantalum,molybdenum, etc. The can is typically two hemispheres, one which isslightly larger to accept the other being slid inside of it to fullyenclosed the diamond feedstock. A rebated area or lip is provided in thelarger can so that the smaller can will satisfactorily fit therein. Theseam of the can is sealed with an appropriate sealant such as dryhexagonal boronitride or a synthetic compression medium. The sealantforms a barrier that prevents the salt pressure medium from penetratingthe can. The can seam may also be welded by plasma, laser, or electronbeam processes.

An appropriately shaped pair of salt domes 1304 and 1307 surround thecan 1310 containing the diamond feedstock 1306. In the example shown,the salt domes each have a heminon-planar cavity 1305 and 1308 forreceiving the can 1310 containing the non-planar diamond feedstock 1306.The salt domes and the can and diamond feedstock are assembled togetherso that the salt domes encase the diamond feedstock. A pair ofcylindrical salt disks 1303 and 1309 are assembled on the exterior ofthe salt domes 1304 and 1307. All of the aforementioned components fitwithin the bore 1302 of the pressure medium cube 1301.

The entire pyrocube assembly is placed into a press and pressurizedunder appropriate pressure (such as about 40-68 Kbar) and for anappropriate although brief duration to precompress the diamond andprepare it for sintering. No heat is necessary for this step.

Mold Releases

When making non-planar shapes, it may be desirable to use a mold in thesintering process to produce the desired net shape. CoCr metal may usedas a mold release in forming shaped diamond or other superhard products.Sintering the superhard powder feed stocks to a substrate, the object ofwhich is to lend support to the resulting superhard table, may beutilized to produce standard Polycrystalline Diamond Compact (PDC) andPolycrystalline Cubic Boron Nitride (PCBN) parts. However, in someapplications, it is desired to remove the diamond table from thesubstrate.

Referring to FIG. 14, a diamond layer 1402 and 1403 has been sintered toa substrate 1401 at an interface 1404. The interface 1404 must be brokento result in free standing diamond if the substrate is not required inthe final product. A mold release may be used to remove the substratefrom the diamond table. If CoCr alloy is used for the substrate, thenthe CoCr itself serves as a mold release, as well as serving as asolvent-catalyst metal. CoCr works well as a mold release because itsCoefficient of Thermal Expansion (CTE) is dramatically different thanthat of sintered PDC or PCBN 3. Because of the large disparity in theCTE's between PDC and PCBN and CoCr, high stress is formed at theinterface 1501 between these two materials as shown in FIG. 15. Thestress that is formed is greater than the bond energy between the twomaterials. When the stress is greater than the bond energy, a crack isformed at the point of highest stress. The crack then propagatesfollowing the narrow region of high stress concentrated at theinterface. Referring to FIG. 16, in this way, the CoCr substrate 1601will separate from the PCD or PCBN 1602 that was sintered around it,regardless of the shape of the interface.

Materials other than CoCr can be used as a mold release. These materialsinclude those metals with high CTE's and, in particular, those that arenot good carbide formers. These are, for example, Co, Ni, CoCr, CoFe,CoNi, Fe, steel, etc.

Gradient Layers and Stress Modifiers

Gradient layers and stress modifiers may be used in the making ofsuperhard constructs. Gradient layers may be used to achieve any of thefollowing objectives:

Improve the “sweep” of solvent metal into the outer layer of superhardmaterial and to control the amount of solvent metal introduced forsintering into said outer layer.

Provide a “sweep” source to flush out impurities for deposit on thesurface of the outer layer of superhard material and/or chemicalattachment/combination with the refractory containment cans.

Control the Bulk Modulus of the various gradient layers and therebycontrol the overall dilatation of the construct during the sinteringprocess.

Affect the “Coefficient of Thermal Expansion” (CTE) of each of thevarious layers by changing the ratio of metal or carbides to diamond,PCBN or other Superhard materials to reduce the CTE of an individualgradient layer.

Allow for the control of structural stress fields through the variouslevels of gradient layers to optimize the overall construct.

Change the direction of stress tensors to improve the outer Superhardlayer, e.g., direct the tensor vectors toward the center of a sphericalconstruct to place the outer layer diamond into compression, orconversely, direct the tensor vectors from the center of the constructto reduce interface stresses between the various gradient layers.

Improve the overall structural stress compliance to external or internalloads by providing a construct that has substantially reducedbrittleness and increased toughness wherein loads are transferredthrough the construct without crack initiation and propagation.

Referring to FIG. 17, The liquid sintering phase of PolycrystallineDiamond (PDC) and Polycrystalline Cubic Boron Nitride (PCBN) istypically accomplished by mixing the solvent sintering metal 1701directly with the Diamond or PCBN powders 1702 prior to the “HighTemperature High Pressure (HPHT) pressing, or (referring to FIG. 18)“sweeping” the solvent metal 1802 from a substrate 1801 into feedstockpowders from the adjacent substrate during HPHT. The very best highquality PDC or PCBN is created using the “sweep” process.

There are several theories related to the increased PDC and CBH qualitywhen using the sweep method. However, most of those familiar with thefield agree that allowing the sintering metal to “sweep” from thesubstrate material provides a “wave front” of sintering metal thatquickly “wets” and dissolves the diamond or CBN and uses only as muchmetal as required to precipitate Diamond or PCBN particle-to-particlebonding. Whereas in a “premixed” environment the metal “blinds off” theparticle-to particle reaction because too much metal is present, orconversely, not enough metal is present to ensure the optimal reaction.

Furthermore, it is felt that the “wave front” of metal sweeping throughthe powder matrix also carries away impurities that would otherwiseimpede the formation of high quality PDC of PCBN. These impurities arenormally “pushed” ahead of the sintering metal “wave front” and aredeposited in pools adjacent to the refractory containment cans. FIG. 19depicts the substrate 1904, the wavefront 1903, and the feedstockcrystals or powder 1902 which the wavefront will sweep through 1901.Certain refractory material such as Niobium, Molybdenum, and Zirconiumcan act as “getters” which combine with the impurities as they immergefrom the matrix giving additional assistance in the creation of highquality end products.

While there are compelling reasons to use the “sweep” process insintering PDC and PCBN there are also problems that arise out of itsuse. For example, not all substrate metals are as controllable as othersas to the quantity of material that is delivered and ultimately utilizedby the powder matrix during sintering. Cobalt metal (6 to 13% by volume)sweeping from cemented tungsten carbide is very controllable when usedagainst diamond or PCBN powders ranging from 1 to 40 microns particlesized. On the other hand, Cobalt Chrome Molybdenum (CoCrMo) that isuseful as a solvent metal to make PDC for some applications overwhelmsthe same PDC matrix with CoCrMo metal in a pure sweep process sometimesproducing inferior quality PDC. The fact that the CoCrMo has a lowermelting point than cobalt, and further that there is an inexhaustiblesupply when using a solid CoCrMo substrate adjacent to the PDC matrix,creates a non-controllable processing condition.

In some applications where it is necessary to use sintering metals sucha CoCrMo that can not be “swept” from a cemented carbide product, it isnecessary to provide a simulated substrate against the PDC powders thatprovides a controlled release and limited supply of CoCrMo for theprocess.

These “simulated” substrates have been developed in the forms of“gradient” layers of mixtures of diamond, carbides, and metals toproduce the desired “sweep” affect for sintering the outer layer of PDC.The first “gradient layer” (just adjacent to the outer or primarydiamond layer which will act as the bearing or wear surface) can beprepared using a mixture of Diamond, Cr₃C₂, and CoCrMo. Depending of thesize fraction of the diamond powder used in the outer layer, the firstgradient layers diamond size fraction and metal content is adjusted forthe optimal sintering conditions.

Where a “simulated” substrate is used, it has been discovered that oftena small amount of solvent metal, in this case CoCrMo must be added tothe outside diamond layer as catalyst to “kick-off” the sinteringreaction.

One embodiment utilizes the mix ranges for the outer 2001 and inner 2002gradient layers of FIG. 20 that are listed in Table 9.

TABLE 9 Diamond Diamond Gradient (Vol. (Size Cr₃C₂ CoCrMo LayersPercent) Fraction-μm) (Vol. Percent) (Vol. Percent) Outer 92 25 0 8Inner 70 40 10 20

The use of gradient layers with solid layers of metal allows thedesigner to match the Bulk Modulus to the Coefficient of ThermalExpansion (CTE) of various features of the construct to counteractdilatory forces encountered during the HTHP phase of the sinteringprocess. For example, in a spherical construct as the pressure increasesthe metals in the construct are compressed or dilated radially towardthe center of the sphere. Conversely, as the sintering temperatureincreases the metal expands radially away from the center of the sphere.Unless these forces are balanced in some way, the compressive dilatoryforces will initiate cracks in the outer diamond layer and cause theconstruct to be unusable.

Typically, changes in bulk modulus of solid metal features in theconstruct are controlled by selecting metals with a compatible modulusof elasticity. The thickness and other sizing features are alsoimportant. CTE, on the other hand, is changed by the addition of diamondor other carbides to the gradient layers.

One embodiment, depicted in FIG. 21, involves the use of two gradientouter layers 2101 and 2102, a solid titanium layer 2103 and an innerCoCrMo sphere 2104. In this embodiment the first gradient layer providesa “sweep source” of biocompatible CoCrMo solvent metal to the outerdiamond layer. The solid Titanium layer provides a dilatory source thatoffsets the CTE from the solid CoCrMo center ball and keeps it from“pulling away” from the Titanium/CoCrMo interface as the sinteringpressure and temperature go from the 65 Kbar and 1400° C. sinteringrange to 1 bar and room temperature.

Where two or more powder based gradient layers are to be used in theconstruct it becomes increasingly important to control the CTE of eachlayer to ensure structural integrity following sintering. During thesintering process stresses are induced along the interface between eachof the gradient layers. These high stresses are a direct result of thedifferences in the CTE between any two adjacent layers. To reduce thesestresses one or both of the layer materials CTE's must be modified.

The CTE of the a substrate can be modified by either changing to asubstrate with a CTE close to that of diamond (an example is the use ofcemented Tungsten Carbide, where the CTE of Diamond is approximately 1.8μm/m-° C. and Cemented Tungsten Carbide is Approximately 4.4 μm/m-° C.),or in the case of powdered layers, by adding a low CTE material to thesubstrate layer itself. That is, making a mixture of two or morematerials, one or more of which will alter the CTE of the substratelayer.

Metal powders can be mixed with diamond or other superhard materials toproduce a material with a CTE close to that of diamond and thus producestresses low enough following sintering to prevent delamination of thelayers at their interfaces. Experimental data shows that the CTEaltering materials will not generally react with each other, whichallows the investigator to predict the outcome of the intermediate CTEfor each gradient level.

The desired CTE is obtained by mixing specific quantities of twomaterials according to the rule of mixtures. Table 10 shows the changein CTE between two materials, A and B as a function of composition(Volume Percent). In this example, materials A and B have CTE's of 150and 600 μIn./In.-° F. respectively. By adding 50 mol % of A to 50 mol %of B the resulting CTE is 375 μin/in-° F.

One or more of the following component processes is incorporated intothe mold release system:

An intermediate layer of material between the polycrystalline diamondcompact part and the mould that prevents bonding of the polycrystallinediamond compact to the mould surface.

A mold material that does not bond to the polycrystalline diamondcompact under the conditions of synthesis.

A mold material that, in the final stages of, or at the conclusion of,the polycrystalline diamond compact synthesis cycle either contractsaway from the polycrystalline diamond compact in the case of a netconcave polycrystalline diamond compact geometry, or expands away fromthe polycrystalline diamond compact in the case of a net convexpolycrystalline diamond compact geometry.

The mold shape can also act, simultaneously as a source of sweep metaluseful in the polycrystalline diamond compact synthesis process.

As an example, a mold release system may be utilized in manufacturing apolycrystalline diamond compact by employing a negative shape of thedesired geometry to produce heminon-planar parts. The mold surfacecontracts away from the final net concave geometry, the mold surfaceacts as a source of solvent-catalyst metal for the polycrystallinediamond compact synthesis process, and the mold surface has poor bondingproperties to polycrystalline diamond compacts.

TABLE 10 PREDICTED DIMENSIONAL CHANGES IN AN EIGHT INCH LAYEREDCONSTRUCT CTE Total Length Final Dimension A % B % (μ In./In-° F.)Change (In.) (In.) 100 0 150 .0012 7.9988 90 10 195 .0016 7.9984 80 20240 .0019 7.9981 70 30 285 .0023 7.9977 60 40 330 .0026 7.9974 50 50 375.0030 7.9970 40 60 420 .0034 7.9966 30 70 465 .0037 7.9963 20 80 510.0041 7.9959 10 90 555 .0044 7.9956 0 100 600 .0048 7.9952

Referring to FIG. 22, an illustration of how the above CTE modificationworks in a one-dimensional example. The one-dimensional example works aswell in a three-dimensional construct. If the above materials A and Bare packed in alternating layers 2201 and 2202 as shown in FIG. 22,separately in their pure forms, with their CTE's of 150 and 600μIn./In.-° F. respectively, they will contract exactly 150 μIn./In.-° F.and 600 μIn./In.-° F. for every degree decrease in temperature. For aneight inch block of the one inch thick stacked layers the total changein dimension for a one degree decrease in temperature will be:Material A:(4×1 In.)×(0.00015 In./In.-° F.)×1° F.=0.0006 In.Material B:(4×1 In.)×(0.00060 In./In.-° F.)×1)° F.=0.0024 In.

-   -   Total overall length decrease in eight inches=0.0030 In.

By comparison, each of the layers is modified by using a mixture of 50%of A and 50% of B, and all eight layers are stacked into the eight-inchblock configuration shown in FIG. 7. Re-calculation of the overalllength decrease using the new composite CET of 375 μIn./In.-° F. fromTable II shows:Material A+B:(8×1 In.)×(0.000375 In./In.-° F.)×1° F.=0.0030 In.

-   -   Total overall length decrease in eight inches=0.0030 In.

The length decrease in this case was accurately predicted for theone-dimensional construct using one-inch thick layers by using the Ruleof Mixtures.

Metals have very high CTE values as compared to diamond, which has oneof the lowest CTE's of any known material. When metals are used assubstrates for PDC and PCBN sintering considerable stress is developedat the interface. Therefore, mixing low CTE material with thebiocompatible metal for medical implants can be used to reduceinterfacial stresses. One of the best candidate materials is diamonditself. Other materials include refractory metal carbides and bitrides,and some oxides. Borides and silicides would also be good materials froma theoretical standpoint, but may not be biocompatible. The following isa list of candidate materials:

Carbides Silicides Oxynitrides Nitrides Oxides Oxyborides BoridesOxycarbides Carbonitrides

There are other materials and combinations of materials that could beutilized as CTE modifiers.

There are also other factors that also apply to the reduction ofinterface stresses for a particular geometrical construct. The thicknessof the gradient layer, its position in the construct, and the generalshape of the final construct all contribute in interfacial stress tensorreduction. Geometries that are more spherical tend to promote interfacecircumferential failures from positive or negative radial tensors whilegeometries of a cylindrical configuration tend to fail at the layerinterfaces precipitated by bending stress couples.

The design of the gradient layers respecting CTE and the amount ofcontraction the each individual layer will experience during coolingform the HTHP sintering process will largely dictate the direction ofstress tensors in the construct. Generally, the designer will alwaysdesire to have the outer wear layer of superhard material in compressionto prevent delamination and crack propagation. In spherical geometriesthe stress tensors would be directed radially toward the center of thespherical shape giving special attention to the interfacial stresses ateach layer interface to prevent failures at these interfaces as well. Incylindrical geometries the stress tensors would be adjusted to preventstress couples from initiating cracks in either end of the cylinder,especially at the end where the wear surface is present.

The following are embodiments that relates to a spherical geometrywherein combinations of gradient layers and/or solid metal balls areused to control the final outcomes of the constructs. FIG. 23 is anembodiment that shows a spherical construct, which utilizes fivegradient layers wherein the composition of each layer is described inTables 11 and 12:

TABLE 11 Diamond Layer Size Volume Cr3C2 CoCrMo Thickness Layer (μm) %Volume % Volume % (In.) First (Outer Layer) 20 92 8 0 .090 2301 Second2302 40 70 20 20 .104 Third 2303 70 60 20 20 .120 Forth 2304 70 60 26 26.138 Fifth 2305 70 25 37.5 37.5 .154

TABLE 12 Diamond Layer Size Volume Cr3C2 CoCrMo Thickness Layer (μm) %Volume % Volume % (In.) First (Outer Layer) 20 100 0 0 .090 2301 Second2302 40 70 20 20 .104 Third 2304 70 60 20 20 .120 Forth 2304 70 60 26 26.138 Fifth 2305 70 25 37.5 37.5 .154

FIG. 24 is an embodiment that shows a spherical construct, whichutilizes four gradient layers wherein the composition of each layer isdescribed in Tables 13 and 14.

TABLE 13 Diamond Layer Size Volume Cr3C2 CoCrMo Thickness Layer (μm) %Volume % Volume % (In.) First (Outer Layer) 20 92 0 8 .097 2401 Second2402 40 70 10 20 .125 Third 2403 70 60 20 20 .144 Forth 2404 70 50 25 25.240

TABLE 14 Diamond Layer Size Volume Cr3C2 CoCrMo Thickness Layer (μm) %Volume % Volume % (In.) First (Outer Layer) 20 100 0 0 .097 2401 Second2402 40 70 10 20 .125 Third 2403 70 60 20 20 .144 Forth 2404 70 50 25 25.240

FIG. 25 shows an embodiment construct that utilizes a center supportball with gradient layers laid up on the ball and each other to form thecomplete construct. The inner ball of solid metal CoCrMo is encapsulatewith a 0.003 to 0.010 inch thick refractory barrier can to prevent theover saturation of the system with the ball metal during the HTHP phaseof sintering. The composition of each layer is described in Tables 15and 16.

TABLE 15 Diamond Layer Size Volume Cr3C2 CoCrMo Thickness Layer (μm) %Volume % Volume % (In.) First (Outer Layer) 20 92  0  8 .097 2501 Second2502 40 70 10 20 .125 Third 2503 70 60 20 20 .144 CoCrMo Ball 2504 N/AN/A N/A N/A N/A

TABLE 16 Diamond Layer Size Volume Cr3C2 CoCrMo Thickness Layer (μm) %Volume % Volume % (In.) First (Outer Layer) 20 100   0  0 .097 2501Second 2502 40 70 10 20 .125 Third 2503 70 60 20 20 .144 CoCrMo Ball2504 N/A N/A N/A N/A N/A

Predicated on the end use function of the sphere above, the inner ballcould be made of Cemented Tungsten Carbide, Niobium, Nickel, Stainlesssteel, Steel, or one of several other metal or ceramic materials tosuite the designers needs.

Embodiments relating to dome shapes are described as follow:

FIG. 26 shows a dome embodiment construct that utilizes two gradientlayers 2601 and 2602 wherein the composition of each layer is describedin Tables 17 and 18.

TABLE 17 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 94 0 60.05 .200 2602 Second 2601 70 60 20 20 0.05 .125

TABLE 18 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 100 0 00.05 .200 2602 Second 2601 70 60 20 20 0.05 .125

FIG. 27 shows a dome embodiment construct that utilizes two gradientlayers 2701 and 2702 wherein the composition of each layer is describedin Tables 19 and 20:

TABLE 19 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 94 0 60.05 .128 2702 Second 2701 70 60 20 20 0.05 .230

TABLE 20 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 100 0 00.05 .128 2702 Second 2701 70 60 20 20 0.05 .230

FIG. 28 shows a dome embodiment construct that utilizes three gradientlayers 2801, 2802 and 2803 where the composition of each layer isdescribed in Tables 21 and 22:

TABLE 21 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 96 0 40.05 .168 2801 Second 2802 40 80 10 10 0.05 .060 Third 2803 70 60 20 200.05 .130

TABLE 22 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 100 0 00.05 .168 2801 Second 2802 40 80 10 10 0.05 .060 Third 2803 70 60 20 200.05 .130

FIG. 29 shows a dome embodiment construct that utilizes three gradientlayers 2901, 2902 and 9803 wherein the composition of each layer isdescribed in Tables 23 and 24:

TABLE 23 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 96 0 40.05 .065 2901 Second 2902 40 80 10 10 0.05 .050 Third 2903 70 60 20 200.05 .243

TABLE 24 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 100 0 00.05 .065 2901 Second 2902 40 80 10 10 0.05 .050 Third 2903 70 60 20 200.05 .243

Embodiments relating to Flat Cylindrical shapes are described asfollows:

FIG. 30 shows a flat cylindrical embodiment construct that utilizes twogradient layers 3001 and 3002 wherein the composition of each layer isdescribed in Tables 25 and 26:

TABLE 25 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 94 0 60.05 3001 Second 3001 70 60 20 20 0.05

TABLE 26 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 100 0 00.05 3001 Second 3002 70 60 20 20 0.05

FIG. 31 shows a flat cylindrical embodiment construct that utilizesthree gradient layers 3101, 3102, 3103 wherein the composition of eachlayer is described in Tables 27 and 28:

TABLE 27 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 96 0 40.05 3101 Second 3102 40 80 10 10 0.05 Third 3103 70 60 20 20 0.05

TABLE 28 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 100 0 60.05 3101 Second 3102 40 80 10 10 0.05 Third 3103 70 60 20 20 0.05

FIG. 32 shows a flat cylindrical embodiment construct that utilizesthree gradient layers 3201, 3202, 3203 laid up on a CoCrMo substrate3204. The cylindrical substrate of solid metal CoCrMo is encapsulatewith a 0.003 to 0.010 inch thick refractory barrier can 3205 to preventthe over saturation of the system with the substrate metal during theHTHP phase of sintering. The composition of each layer is described inTables 29 and 30:

TABLE 29 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 96  0 4 0.05 3201 Second 3202 40 80 10 10 0.05 Third 3203 70 60 20 20 0.05CoCrMo N/A N/A N/A N/A N/A Substrate 3204

TABLE 30 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 100   0 0 0.05 3201 Second 3202 40 80 10 10 0.05 Third 3203 70 60 20 20 0.05CoCrMo N/A N/A N/A N/A N/A Substrate 3204

Predicated on the end use function of the cylinder shape of FIG. 32 theinner substrate could be made of Cemented Tungsten Carbide, Niobium,Nickel, Stainless steel, Steel, or one of several other metal or ceramicmaterials to suite the designers needs.

Embodiments relating to Flat Cylindrical Shapes with Formed-in-PlaceConcave Features are described as follow:

FIG. 33 show an embodiment of a flat cylindrical shape with a formed inplace concave trough 3303 that utilizes two gradient layers 3301 and3302 wherein the composition of each layer is described in Tables 31 and32:

TABLE 31 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 04 0 60.05 .156 3301 Second 3302 70 60 20 20 0.05 .060 Filler Support 70 60 2020 0.05 N/A 3303

TABLE 32 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 100 0 00.05 .156 3301 Second 3302 70 60 20 20 0.05 .060 Filler Support 70 60 2020 0.05 N/A 3303

FIG. 34 shows an embodiment of a flat cylindrical shape with a formed inplace concave trough 3402 that utilizes two gradient layers 3401 and3402 wherein the composition of each layer is described in Tables 33 and34:

TABLE 33 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 94 0 60.05 .156 3401 Second 3402 70 60 20 20 0.05 .060 Filler Support 70 60 2020 0.05 N/A 3403

TABLE 34 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 100 0 00.05 .156 3401 Second 3402 70 60 20 20 0.05 .060 Filler Support 70 60 2020 0.05 N/A 3403

FIG. 35 shows an embodiment of a flat cylindrical shape with a formed inplace concave 3504 trough that utilizes three gradient layers 3501,3502, 2503 wherein the composition of each layer is described in Tables35 and 36:

TABLE 35 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 96 0 40.05 .110 3501 Second 3502 40 80 10 10 0.05 .040 Third 3503 70 60 20 200.05 .057 Filler Support 70 60 20 20 0.05 N/A 3504

TABLE 36 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 100 0 00.05 .110 3501 Second 3502 40 80 10 10 0.05 .040 Third 3503 70 60 20 200.05 .057 Filler Support 70 60 20 20 0.05 N/A 3504

FIG. 36 shows an embodiment of a flat cylindrical shape with a formed inplace concave trough 3604 that utilizes three gradient layers 3601,3602, 3603 wherein the composition of each layer is described in Tables37 and 38:

TABLE 37 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 96 0 40.05 .110 3601 Second 3602 40 80 10 10 0.05 .040 Third 3603 70 60 20 200.05 .057 Filler Support 70 60 20 20 0.05 N/A 3604

TABLE 38 Diamond Layer Size Cr3C2 CoCrMo TiCTiN Thickness Layer (μm)Volume % Volume % Volume % Volume % (In.) First (Outer Layer) 20 100 0 00.05 .110 3601 Second 3602 40 80 10 10 0.05 .040 Third 3603 70 60 20 200.05 .057 Filler Support 70 60 20 20 0.05 N/A 3604Prepare Heater Assembly

In order to sinter the assembled and loaded diamond feedstock describedabove into polycrystalline diamond, both heat and pressure are required.Heat is provided electrically as the part undergoes pressure in a press.A heater assembly is used to provide the required heat.

A refractory metal can containing loaded and precompressed diamondfeedstock is placed into a heater assembly. Salt domes are used toencase the can. The salt domes used may be white salt (NaCl) that isprecompressed to at least about 90-95% of theoretical density. Thisdensity of the salt is desired to preserve high pressures of thesintering system and to maintain geometrical stability of themanufactured part. The salt domes and can are placed into a graphiteheater tube assembly. The salt and graphite components of the heaterassembly may be baked in a vacuum oven at greater than 100 degreesCelsius and at a vacuum of at least 23 torr for about 1 hour in order toeliminate adsorbed water prior to loading in the heater assembly. Othermaterials which may be used in construction of a heater assembly includesolid or foil graphite, amorphous carbon, pyrolitic carbon, refractorymetals and high electrical resistant metals.

Once electrical power is supplied to the heater tube, it will generateheat required for polycrystalline diamond formation in the highpressure/high temperature pressing operation.

Preparation of Pressure Assembly for Sintering

Once a heater assembly has been prepared, it is placed into a pressureassembly for sintering in a press under high pressure and hightemperature. A cubic press or a belt press may be used for this purpose,with the pressure assembly differing somewhat depending on the type ofpress used. The pressure assembly is intended to receive pressure from apress and transfer it to the diamond feedstock so that sintering of thediamond may occur under isostatic conditions.

If a cubic press is used, then a cube of suitable pressure transfermedia such as pyrophillite will contain the heater assembly. Cellpressure medium would be used if sintering were to take place in a beltpress. Salt may be used as a pressure transfer media between the cubeand the heater assembly. Thermocouples may be used on the cube tomonitor temperature during sintering. The cube with the heater assemblyinside of it is considered a pressure assembly, and is place into apress a press for sintering.

Sintering of Feedstock into Polycrystalline Diamond

The pressure assembly described above containing a refractory metal canthat has diamond feedstock loaded and precompressed within is placedinto an appropriate press. The type of press used at the time of thedevices may be a cubic press (i.e., the press has six anvil faces) fortransmitting high pressure to the assembly along 3 axes from sixdifferent directions. Alternatively, a belt press and a cylindrical cellcan be used to obtain similar results. Other presses may be used aswell. Referring to FIG. 37, a representation of the 6 anvils of a cubicpress 3720 is provided. The anvils 3721, 3722, 3723, 3724, 3725 and 3726are situated around a pressure assembly 3730.

To prepare for sintering, the entire pressure assembly is loaded into apress and initially pressurized to about 40-68 Kbars. The pressure to beused depends on the product to be manufactured and must be determinedempirically. Then electrical power may be added to the pressure assemblyin order to reach a temperature in the range of less than about 1145 or1200 to more than about 1500 degrees Celsius. About 5800 watts ofelectrical power may be used at two opposing anvil faces, creating thecurrent flow required for the heater assembly to generate the desiredlevel of heat. Once the desired temperature is reached, the pressureassembly is subjected to pressure of about 1 million pounds per squareinch at the anvil face. The components of the pressure assembly transmitpressure to the diamond feedstock. These conditions may be maintainedfor about 3-12 minutes, but could be from less than 1 minute to morethan 30 minutes. The sintering of polycrystalline diamond compacts takesplace in an isostatic environment where the pressure transfer componentsare permitted only to change in volume but are not permitted tootherwise deform. Once the sintering cycle is complete, about a 90second cool down period is allowed, and then pressure is removed. Thepolycrystalline diamond compact is then removed for finishing.

Removal of a sintered polycrystalline diamond compact having a curved,compound or complex shape from a pressure assembly is simple due to thedifferences in material properties between diamond and the surroundingmetals in some embodiments of the devices. This is generally referred toas the mold release system of the devices.

Removal of Solvent-Catalyst Metal from PVD

If desired, the solvent-catalyst metal remaining in interstitial spacesof the sintered polycrystalline diamond may be removed. Such removal isaccomplished by chemical leaching as is known in the art. Aftersolvent-catalyst metal has been removed from the interstitial spaces inthe diamond table, the diamond table will have greater stability at hightemperatures. This is because there is no catalyst for the diamond toreact with and break down.

After leaching solvent-catalyst metal from the diamond table, it may bereplaced by another metal, metal or metal compound in order to formthermally stable diamond that is stronger than leached polycrystallinediamond. If it is intended to weld synthetic diamond or apolycrystalline diamond compact to a substrate or to another surfacesuch as by inertia welding, it may be desirable to use thermally stablediamond due to its resistance to heat generated by the welding process.

Finishing Methods and Apparatuses

Once a polycrystalline diamond compact has been sintered, a mechanicalfinishing process may be employed to prepare the final product. Thefinishing steps explained below are described with respect to finishinga polycrystalline diamond compact, but they could be used to finish anyother surface or any other type of component.

Prior to the devices herein, the synthetic diamond industry was facedwith the problem of finishing flat surfaces and thin edges of diamondcompacts. Methods for removal of large amounts of diamond fromnon-planar surfaces or finishing those surfaces to high degrees ofaccuracy for sphericity, size and surface finish had not been developedin the past.

Finishing of Superhard Cylindrical and Flat Forms.

In order to provide a greater perspective on finishing techniques forcurved and non-planar superhard surfaces for articulatingdiamond-surfaced spinal implants, a description of other finishingtechniques is provided.

Lapping.

A wet slurry of diamond grit on cast iron or copper rotating plates areused to remove material on larger flat surfaces (e.g., up to about 70mm. in diameter). End coated cylinders of size ranging from about 3 mmto about 70 mm may also be lapped to create flat surfaces. Lapping isgenerally slow and not dimensionally controllable for depth and layerthickness, although flatness and surface finishes can be held to veryclose tolerances.

Grinding.

Diamond impregnated grinding wheels are used to shape cylindrical andflat surfaces. Grinding wheels are usually resin bonded in a variety ofdifferent shapes depending on the type of material removal required(i.e., cylindrical centerless grinding or edge grinding).Polycrystalline diamond compacts are difficult to grind, and largepolycrystalline diamond compact surfaces are nearly impossible to grind.Consequently, it is desirable to keep grinding to a minimum, andgrinding is usually confined to a narrow edge or perimeter or to thesharpening of a sized PDC end-coated cylinder or machine tool insert.

Electro Spark Discharge Grinding (EDG).

Rough machining of polycrystalline diamond compact may be accomplishedwith electro spark discharge grinding (“EDG”) on large diameter (e.g.,up to about 70 mm.) flat surfaces. This technology typically involvesthe use of a rotating carbon wheel with a positive electrical currentrunning against a polycrystalline diamond compact flat surface with anegative electrical potential. The automatic controls of the EDG machinemaintain proper electrical erosion of the polycrystalline diamondcompact material by controlling variables such as spark frequency,voltage and others. EDG is typically a more efficient method forremoving larger volumes of diamond than lapping or grinding. After EDG,the surface must be finish lapped or ground to remove what is referredto as the heat affected area or re-cast layer left by EDG.

Wire Electrical Discharge Machining (WEDM).

WEDM is used to cut superhard parts of various shapes and sizes fromlarger cylinders or flat pieces. Typically, cutting tips and inserts formachine tools and re-shaping cutters for oil well drilling bitsrepresent the greatest use for WEDM in PDC finishing.

Polishing.

Polishing superhard surfaces for articulating diamond-surfaced spinalimplants to very high tolerances may be accomplished by diamondimpregnated high speed polishing machines. The combination of high speedand high friction temperatures tends to burnish a PDC surface finishedby this method, while maintaining high degrees of flatness, therebyproducing a mirror-like appearance with precise dimensional accuracy.

Finishing a Non-Planar Geometry

Finishing a non-planar surface (concave non-planar or convex non-planar)presents a greater problem than finishing a flat surface or the roundededge of a cylinder. The total surface area of a sphere to be finishedcompared to the total surface area of a round end of a cylinder of likeradius is four (4) times greater, resulting in the need to remove four(4) times the amount of polycrystalline diamond compact material. Thenature of a non-planar surface makes traditional processing techniquessuch as lapping, grinding and others unusable because they are adaptedto flat and cylindrical surfaces. The contact point on a sphere shouldbe point contact that is tangential to the edge of the sphere, resultingin a smaller amount of material removed per unit of time, and aproportional increase in finishing time required. Also, the design andtypes of processing equipment and tooling required for finishingnon-planar objects must be more accurate and must function to closertolerances than those for other shapes. Non-planar finishing equipmentalso requires greater degrees of adjustment for positioning theworkpiece and tool ingress and egress.

The following are steps that may be performed in order to finish anon-planar, rounded or arcuate surface.

1.) Rough Machining.

Initially roughing out the dimensions of the surface using a specializedelectrical discharge machining apparatus may be performed. Referring toFIG. 38, roughing a polycrystalline diamond compact sphere 3803 isdepicted. A rotator 3802 is provided that is continuously rotatableabout its longitudinal axis (the z axis depicted). The sphere 3803 to beroughed is attached to a spindle of the rotator 3802. An electrode 3801is provided with a contact end 3801A that is shaped to accommodate thepart to be roughed. In this case the contact end 3801A has a partiallynon-planar shape. The electrode 3801 is rotated continuously about itslongitudinal axis (the y axis depicted). Angular orientation of thelongitudinal axis y of the electrode 3801 with respect to thelongitudinal axis z of the rotator 3802 at a desired angle β is adjustedto cause the electrode 3801 to remove material from the entirenon-planar surface of the ball 3803 as desired.

Thus, the electrode 3801 and the sphere 3803 are rotating aboutdifferent axes. Adjustment of the axes can be used to achieve nearperfect non-planar movement of the part to be roughed. Consequently, anearly perfect non-planar part results from this process. This methodproduces polycrystalline diamond compact non-planar surfaces with a highdegree of sphericity and cut to very close tolerances. By controllingthe amount of current introduced to the erosion process, the depth andamount of the heat affected zone can be minimized. In the case of apolycrystalline diamond compact, the heat affected zone can be kept toabout 3 to 5 microns in depth and is easily removed by grinding andpolishing with diamond impregnated grinding and polishing wheels.

Referring to FIG. 39, roughing a convex non-planar polycrystallinediamond compact 1003 such as an articulating diamond-surfaced spinalimplant is depicted. A rotator 3902 is provided that is continuouslyrotatable about its longitudinal axis (the z axis depicted). The part3903 to be roughed is attached to a spindle of the rotator 3902. Anelectrode 3901 is provided with a contact end 3901A that is shaped toaccommodate the part to be roughed. The electrode 3901 is continuouslyrotatable about its longitudinal axis (the y axis depicted). Angularorientation of the longitudinal axis y of the electrode 3901 withrespect to the longitudinal axis z of the rotator 3902 at a desiredangle β is adjusted to cause the electrode 3901 to remove material fromthe entire non-planar surface of the articulating diamond-surfacedspinal implant 3903 as desired.

In some embodiments of the devices, multiple electro discharge machineelectrodes will be used in succession in order to machine a part. Abattery of electro discharge machines may be employed to carry this outin assembly line fashion. Further refinements to machining processes andapparatuses are described below.

Complex positive or negative relief (concave or convex) forms can bemachined into Polycrystalline Diamond Compacts (PDC) or Polycrystallinecubic Boron Nitride (PCBN) parts. This a standard Electrical DischargeMachining (EDM) CNC machining center and suitably machined electrodesaccomplish the desired forms.

FIG. 40 (side view) and FIG. 40 a (end view) show an electrode 4001 witha convex form 4002 machined on the active end of the electrode 4001, andthe electrode base 4005. FIG. 41 (cross section at 41-41) and FIG. 41 ashow an electrode 4101 with a concave form 4102 and base 4105. Theopposite ends of the electrodes are provided with an attachmentmechanism at the base 4105 suitable for the particular EDM machine beingutilized. There are a variety of electrode materials that can beutilized such a copper, copper tungsten, graphite, and combinations ofgraphite and metal mixes. Materials best suited for machining PDC andPCBN are copper tungsten for roughing and pure graphite, or graphitecopper tungsten mixes. Not all EDM machines are capable of machining PDCand PCBN. Only those equipped with capacitor discharge power suppliescan generate spark intensities with enough power to efficiently erodethese materials.

The actual size of the machined relief form is usually machinedundersized to allow for a suitable spark gap for the burning/erosionprocess to take place. Each spark gap length dictates a set of machiningparameters that must be set by the machine operator to ensure efficientelectrical discharge erosion of the material to be removed. Normally,two to four electrodes are prepared with different spark gap allowances.For example, an electrode using a 0.006 In. spark gap could be preparedfor “roughing,” and an “interim” electrode at 0.002 In. spark gap, and“finishing” electrode at 0.0005 In. spark gap. In each case themachining voltage (V), peak amperage (AP), pulse duration (P), referencefrequency (RF), pulse duration (A), retract duration (R), under-the-cutduration (U), and servo voltage (SV) must be set up within the machinescontrol system.

FIG. 42 shows an EDM relief form 4201 sinking operation in a PDC insertpart 4202. Table 39 describes the settings for the using a coppertungsten electrode 4203 for roughing and a graphite/copper tungstenelectrode for finishing. The spark gap 4204 is also depicted.

TABLE 39 Electrode Spark Gap 4203 4204 V AP P RF A R U SV Roughing .006−2 7 13 56 9 0 9 50 Finishing .001 −5 4 2 60 2 0 9 55

Those familiar with the field of EDM machining will recognize thatvariations in the parameters show will be required based on theelectrode configuration, electrode wear rates desired, and surfacefinishes required. Generally, higher machining rates, i.e., highervalues of “V” and “AP” produce higher rates of discharge erosion, butconversely rougher surface finishes.

Obtaining very smooth and accurate finishes also requires the use of aproper dielectric machining fluid. Synthetic hydrocarbons with satelliteelectrodes as disclosed in U.S. Pat. No. 5,773,782, which is herebyincorporated by reference, appear to assist in obtaining high qualitysurface finishes.

FIG. 43 shows an embodiment wherein a single ball-nosed (sphericalradiused) EDM electrode 4301 is used to form a concave relief form 4303in a PDC or PCBN part 4302. The electrode 4301 is plunged verticallyinto the part 4302 and then moved laterally to accomplish the rest ofthe desired shape. By programming a CNC system EDM electrode “cuttingpath” of the EDM machine, an infinite variety of concave or convexshapes can be machined. Controlling the rate of “down” plunging and“lateral” cross cutting, and using the correct EDM material will dictatethe quality of the size dimensions and surface finishes obtained.

2.) Finish Grinding and Polishing.

Once the non-planar surface (whether concave or convex) has been roughmachined as described above or by other methods, finish grinding andpolishing of a part can take place. Grinding is intended to remove theheat affected zone in the polycrystalline diamond compact material leftbehind by electrodes.

In some embodiments of the devices, grinding utilizes a grit sizeranging from 100 to 150 according to standard ANSI B74.16-1971 andpolishing utilizes a grit size ranging from 240 to 1500, although gritsize may be selected according to the user's preference. Wheel speed forgrinding should be adjusted by the user to achieve a favorable materialremoval rate, depending on grit size and the material being ground. Asmall amount of experimentation can be used to determine appropriatewheel speed for grinding. Once the spherical surface (whether concave orconvex) has been rough machined as described above or by other methods,finish grinding and polishing of a part can take place. Grinding isintended to remove the heat affected zone in the polycrystalline diamondcompact material left behind by electrodes. Use of the same rotationalgeometry as depicted in FIGS. 9 and 10 allows sphericity of the part tobe maintained while improving its surface finish characteristics.

Referring to FIG. 44, it can be seen that a rotator 4401 holds a part tobe finished 4403, in this case a convex sphere, by use of a spindle. Therotator 4401 is rotated continuously about its longitudinal axis (the zaxis). A grinding or polishing wheel 4402 is provided is rotatedcontinuously about its longitudinal axis (the x axis). The moving part4403 is contacted with the moving grinding or polishing wheel 4402. Theangular orientation β of the rotator 4401 with respect to the grindingor polishing wheel 4402 may be adjusted and oscillated to effectgrinding or polishing of the part (ball or socket) across its entiresurface and to maintain sphericity.

Referring to FIG. 45, it can be seen that a rotator 4501 holds a part tobe finished 4503, in this case a convex spherical cup or race, by use ofa spindle. The rotator 4501 is rotated continuously about itslongitudinal axis (the z axis). A grinding or polishing wheel 4502 isprovided that is continuously rotatable about its longitudinal axis (thex axis). The moving part 4503 is contacted with the moving grinding orpolishing wheel 4502. The angular orientation β of the rotator 4501 withrespect to the grinding or polishing wheel 4502 may be adjusted andoscillated if required to effect grinding or polishing of the partacross the spherical portion of it surface.

In one embodiment, grinding utilizes a grit size ranging from 100 to 150according to standard ANSI B74.16-1971 and polishing utilizes a gritsize ranging from 240 to 1500, although grit size may be selectedaccording to the user's preference. Wheel speed for grinding should beadjusted by the user to achieve a favorable material removal rate,depending on grit size and the material being ground. A small amount ofexperimentation can be used to determine appropriate wheel speed forgrinding.

As desired, a diamond abrasive hollow grill may be used for polishingdiamond or superhard bearing surfaces. A diamond abrasive hollow grillincludes a hollow tube with a diamond matrix of metal, ceramic and resin(polymer) is found.

If a diamond surface is being polished, then the wheel speed forpolishing may be adjusted to cause a temperature increase or heatbuildup on the diamond surface. This heat buildup will cause burnishingof the diamond crystals to create a very smooth and mirror-like lowfriction surface. Actual material removal during polishing of diamond isnot as important as removal sub-micron sized asperities in the surfaceby a high temperature burnishing action of diamond particles rubbingagainst each other. A surface speed of 6000 feet per minute minimum isgenerally required together with a high degree of pressure to carry outburnishing. Surface speeds of 4000 to 10,000 feet per minute arebelieved to be the most desirable range. Depending on pressure appliedto the diamond being polished, polishing may be carried out at fromabout 500 linear feet per minute and 20,000 linear feet per minute.

Pressure must be applied to the workpiece in order to raise thetemperature of the part being polished and thus to achieve the mostdesired mirror-like polish, but temperature should not be increased tothe point that it causes complete degradation of the resin bond thatholds the diamond polishing wheel matrix together, or resin will bedeposited on the diamond. Excessive heat will also unnecessarily degradethe surface of the diamond.

Maintaining a constant flow of coolant (such as water) across thediamond surface being polished, maintaining an appropriate wheel speedsuch as 6000 linear feet per minute, applying sufficient pressureagainst the diamond to cause heat buildup but not so much as to degradethe wheel or damage the diamond, and timing the polishing appropriatelyare all important and must all be determined and adjusted according tothe particular equipment being used and the particular part beingpolished. Generally the surface temperature of the diamond beingpolished should not be permitted to rise above 800 degrees Celsius orexcessive degradation of the diamond will occur. Desirable surfacefinishing of the diamond, called burnishing, generally occurs between650 and 750 degrees Celsius.

During polishing it is important to achieve a surface finish that hasthe lowest possible coefficient of friction, thereby providing a lowfriction and long-lasting articulation surface. Preferably, once adiamond or other superhard surface is formed in a bearing component, thesurface is then polished to an Ra value of 0.3 to 0.005 microns.Acceptable polishing will include an Ra value in the range of 0.5 to0.005 microns or less. The parts of the bearing component may bepolished individually before assembly or as a unit after assembly. Othermethods of polishing polycrystalline diamond compacts and othersuperhard materials could be adapted to work with the articulationsurfaces of the invented bearing components, with the objective being toachieve a smooth surface, preferably with an Ra value of 0.01-0.005microns. Further grinding and polishing details are provided below.

FIG. 46 shows a diamond grinding form 4601 mounted to an arbor 4602,which is in turn mounted into the high-speed spindle 4603 of a CNCgrinding machine. The cutting path motion 4604 of the grinding form 4601is controlled by the CNC program allowing the necessary surface coveragerequiring grinding or polishing. The spindle speed is generally relatedto the diameter of the grinding form and the surface speed desired atthe interface with the material 4505 to be removed. The surface speedshould range between 4,000 and 17,000 feet per minuet for both grindingand polishing. For grinding, the basic grinding media for the grindingform should be as “free” cutting as practical with diamond grit sizes inthe range of 80 to 120 microns and concentrations ranging from 75 to125. For polishing the grinding media should not be as “free cutting,”i.e., the grinding form should generally be harder and denser with gritsizes ranging from 120 to 300 microns and concentrations ranging from100 to 150.

Superhard materials can be more readily removed by grinding if theactual area of the material being removed is kept as small as possible.Ideally the bruiting form 4601 should be rotated to create conditions inthe range from 20,000 to 40,000 surface feet per minuet between the part4605 and the bruiting form 4601. Spindle pressure between the part 4605and the bruiting form 4601 operating in a range of 10 to 100 Lbs-forceproducing an interface temperature between 650 and 750 Deg C. isrequired. Cooling water is needed to take away excess heat to keep thepart from failing possible. The simplest way to keep the grind areasmall is to utilize a small cylindrical contact point (usually a ballform, although a radiused end of a cylinder accomplishes the samepurpose), operating against a larger surface area.

FIG. 47 shows the tangential area of contact 4620 between the grindingform 4601 and the substantially larger superhard material 4621. Bycontrolling the path of the grinding form cutter, small grooves 4630(FIG. 48) can be ground into the surface of the superhard material 4621removing the material and leaving small “cusp” 4640 between the adjacentgrooves. As the grooves are cut shallower and closer together the “cusp”4640 become imperceptible to the naked eye and are easily removed bysubsequent polishing operations. The cutter line path of the grindingform cutter should be controlled by programming the CNC system of thegrinding machine to optimize the cusp size, grinding form cutter wear,and material removal rates.

Bruting

Obtaining highly polished surface finishes on Polycrystalline DiamondCompact (PDC), Polycrystalline Cubic Boron Nitride (PBCN), and othersuperhard materials in the range of 0.05 to 0.005 μm can be obtained byrunning PDC form against the surface to be polished. “Bruiting” orrubbing a diamond surface under high pressure and temperature againstanother superhard material degredates or burns away any positiveasperities remaining from previous grinding and polishing operationsproducing a surface finish not obtainable in any other way.

FIG. 49 shows a PDC dome part 4901 on a holder 4904 and being “BruitPolished” using a PDC bruiting form 4902 being rotated in a high-speedspindle 4903. Ideally the bruiting form should be rotated in a rangefrom 20,000 to 40,000 surface feet per minute with the spindle pressureoperating in a range of 10 to 100 Lbs-force producing an interfacetemperature between 650 and 750 Deg C. Cooling water is generallyrequired to take away excess heat to keep the part from failing.

FIG. 50 shows another embodiment of the bruiting polishing techniquewherein the PDC Bruiting form 5001 is controlled through a complexsurface path 5002 by a CNC system of a grinding machine or a CNC Millequipped with a high-speed spindle to control the point of contact 5003of the form 5001 with a superhard component 5004.

Use of Cobalt Chrome Molybdenum (COCRMO) Alloys to AugmentBiocompatability in Polycrystalline Diamond Compacts

Cobalt and Nickel may be used as catalyst metals for sintering diamondpowder to produce sintered polycrystalline diamond compacts. Thetoxicity of both Co and Ni is well documented; however, use of CoCralloys which contain Co and Ni have outstanding corrosion resistance andavoid passing on the toxic effects of Co or Ni alone. Use of CoCrMoalloy as a solvent-catalyst metal in the making of sinteredpolycrystalline diamond compacts yields a biocompatible and corrosionresistant material. Such alloys may be defined as any suitablebiocompatible combination of the following metals: Co, Cr, Ni, Mo, Tiand W. Examples include ASTM F-75, F-799 and F-90. Each of these willserve as a solvent-catalyst metal when sintering diamond. Elementalanalysis of the interstitial metal in PDC made with these alloys hasshown that the composition is substantially more corrosion resistantthan PDC made with Co or Ni alone.

Example Articulating Diamond-Surfaced Spinal Implants

As used herein, the term “articulating” means that the spinal implantpermits some range of motion, in contrast with fusion therapy in whichtwo vertebrae are permanently locked together with respect to eachother. The spinal implants may provide rotation about the axial, coronaland/or sagittal axes and/or translation in the axial plane. The rotationmay permit anterior and posterior bending, lateral bending, and twistingof the torso. The translation may include anterior, posterior andlateral translation. A combination of such rotation and translation isdesired in order to approximate the flexion and extension of a humanspine.

Also, as used herein “diamond-surfaced” means that the spinal implantincludes diamond on at least a portion of one load bearing orarticulation surface. The implant may include diamond located on asubstrate, it may be solid free-standing diamond, or it may be ofanother structure. The diamond may be sintered polycrystalline diamondthat is a free-standing table or a diamond table sintered or otherwiseattached to a substrate.

Spinal Disk Implants with Bearing Surfaces Wear Enhanced by Diamond

The mode of devices included herein includes the enhancement of spinaldisk implants 5100 with bearing surfaces wear-enhanced by theapplication or presence of Poly Crystalline Diamond Compact (PDC). Allof the spinal disk implants FIG. 51 and FIG. 52 including the CervicalDisk (one through seven) 51, the Thoracic Disk (one through twelve) 52,and the Lumbar Disk (one through five) 53 can be enhanced by theapplication of PDC and are included as parts of this devices.

FIGS. 53, 53-1, 53-2, 53-3 and 53-4 show a spinal disk replacementimplant 101 which uses an Ultra High Molecular Weight Polyethylene(UHMWPE) hemispherical dome 5304 running against a cobalt chrome metalconcave cup 5305. The UHMWPE dome insert 5304 is held in place by atongue and groove retainer groove 5306.

FIGS. 54-56 show the disk replacement implant 5101 in a typicalinstallation between two adjacent vertebras 5607, 5608, and FIGS. 55 and56 depict the relative position of the implant 5101 viewed from theaxial plane view, and the coronal plane view. FIG. 57 shows the relativeside-to-side lateral angular motion possible by using a two partcongruent bearing insert 5101. The angle α typically allows a lateralbending range of plus or minus 10 degrees and is centered about the baseof the spinous process. FIG. 58 shows the rotation β 5810 available inthe axial plane which is not limited by the implant 5101 itself, butrather by the surrounding tissue such as muscle and ligaments. FIG. 59shows the flexion angle θ 5911 which is typically 10 to 13 degrees, andthe extension angle φ 5912 of FIG. 60 typically ranging from 5 to 8degrees. A prosthetic spinal disk may permit some or all of theforegoing articulation, in greater or lesser degrees of flexibility.

FIGS. 61 and 61-1 depict spinal disk implant 600102 including the use ofa metal substrate 60013 on which PDC 60014 has been applied. TheSubstrate/PDC assembly 600103 is held in place by a tongue and grooveretainer groove 60015 in the inferior endplate 60016. The mating convexcup 60017 has PDC 60018 applied directly to the superior endplate 60019.

The spinal disk implant 600104 shown in FIGS. 62-1 and 62 shows a solidPDC dome insert 60020 held in place in the inferior endplate 60021 by atongue and groove retainer groove 60022. The mating convex cup 60023 hasPDC 60024 applied directly to the superior endplate 60025.

The PDC dome insert 600105 shown in FIGS. 63 and 63-1 is held in placeby a surrounding injection molded insert base 60026. The molded polymer60026 surrounds the protrusions 60027 formed in the PDC 60028restricting movement and holding it in place. The injected molded/PDCinsert assembly 600106 is held in place in the inferior endplate 60029by a tongue and groove retainer groove 60030. The mating convex cup60031 has PDC 60032 applied directly to the superior endplate 60033.

Spinal disk implant 600107 depicted in FIGS. 64 and 64-1 shows a solidPDC dome insert 60033 installed and held in place by an interference fitbetween the outside diameter 60034 of the dome insert and the receivingbore 60035 in the inferior endplate 60036. The mating convex solid PDCcup insert 60037 is also installed and held in place by an interferencefit between the outside diameter of the cup insert 60038 and thereceiving bore 60039 in the superior endplate 60040. Alternate retainingmethods to hold the PDC inserts 60033 and 60037 in the inferior 60036and superior 60040 endplates could involve the use of brazing, polymerbonding adhesives, retaining screws, or other standard attachmentmethods.

FIGS. 65 through 65-4 show a three part spinal disk implant 600108 withthree components including the inferior endplate 60041, superiorendplate 60042, both of which contain a convex cup receiver 60043, 60044for the domes 60045 and 60046, of the double hemispherical dome centerpart 60047. The two endplates 60041 and 60042 are generally fabricatedform Cobalt Chrome metal but could be fabricated from any otherbiocompatible metal with sufficient wear qualities. The center doubledome part 60047 is fabricated from High Molecular Weight Polyethylene(UHMWPE).

FIG. 66 shows a disk replacement implant 600108 in a typicalinstallation between two adjacent vertebras 60048, 60049, and FIGS. 67and 68 depict the relative position of the implant 600108 viewed fromthe axial plane view, and the coronal plane view.

FIG. 69 shows the relative side-to-side lateral angular motion possibleby using a three part congruent bearing insert 600108. The angles α60050 typically allow a lateral bending range of plus or minus 10degrees. FIG. 70 shows the rotation β 60051 available in the axial planewhich is not limited by the implant 600108 itself, but rather by thesurrounding tissue. FIGS. 71 and 72 shows the flexion angles θ 60052which are typically 10 to 13 degrees, and the extension angle φ 60053FIG. 72 typically ranging from 5 to 8 degrees.

FIGS. 73 and 73-1 show a typical three piece spinal implant 600109 withPDC 60054 and 60055 applied to the inferior endplate 60056 and superiorendplate 60057 to form the convex cup receivers 60059, 60060. The doublehemispherical dome center part 60061 has PDC 60062 applied to form themating domes 60063, 60064 for the cup receivers 60059, 60060.

The three piece spinal implant 600110 shown in FIGS. 74 and 74-1 hasbeen enhanced by applying PDC to the inferior 60065 and superior 60066endplate convex cup receivers 60067, 60068. The PDC dome inserts 60069,60070 have been preformed and finished and then injection molded intothe double dome hemispherical center part 60071. The PDC domes inserts60069, 60070 are retained in place on the center part by the overlap60072 of the injection molded polymer material.

Solid PDC inferior 60073 and superior 60074 end plates are used in thethree piece spinal implant FIGS. 75 and 75-1 600111 and for the doubledome center part 60075. The center PDC double dome part 60075 has beeninjection molded into polymer material to form the complete articulatingcenter part 60076. The overlap 60077 of the injection molded polymermaterial retains the outer ring bumper 60078 onto the solid or freestanding PDC center part 60075.

The spinal implant 600112 of FIGS. 76, 77 and 78 depicts the PDCenhancement of the bearing couple Dome 60079 and the convex cup/trough60080. The PDC dome insert 60079 is installed into the superior endplate60081 and held in place by an interference fit between the outsidediameter 60082 of the dome insert 60079 and the receiving bore 60083 inthe superior endplate 60081. The PDC cup/trough insert 60080 isinstalled into the inferior endplate 60084 and held in place by aninterference fit between the outside diameter 85 of the cup/troughinsert 60080 and the receiving bore 60086 in the inferior endplate60084. Alternate retaining methods to hold the PDC inserts 60079 and60080 in the inferior 60084 and superior 60081 endplates could involvethe use of brazing, polymer bonding adhesives, retaining screws, orother standard attachment methods. The configuration of the cup/troughinsert 60080 allows for not only angular side-to-side motion and flexionand extension motion, but also provides for translational motion X 60086FIG. 77 in the posterior and anterior directions plus or minus 1 mm ormore if desired. The radial sides of the dome 60079 will not be closeenough to the sides of the cup/trough 60080 FIG. 78 to providehydrodynamic support where even minimal bearing clearance has beenprovided, and likewise, the trough ends 60087 will not provide anysupport. Therefore, unlike the fully congruent bearings of the spinalinserts 600200 through 600111, the dome 60079 will be “point loaded” inthe cup/trough 60080 generally promoting extreme bearing loadingconditions. The extreme conditions wrought by non-congruent bearingconfigurations will generally not wear or function well with knownbiocompatible metals. This type of problem, depicted with the spinalimplant 600112, functions extremely well when enhanced by PDC asdescribed above. Test results showing less that 0.3 mg weight loss for30 million unlubricated cycles at five times the anatomical load aretypical. Metal bearings tested under similar conditions would failwithin a few hundred cycles.

FIG. 79 depicts the spinal implant 600113 section view wherein thecongruent bearings concave cup 60088 and the matching dome 60089 havereceived surface enhancement of PCD.

The Spinal implant 114 of FIG. 80A and FIG. 80B depicts the PCD surfaceenhancement 60090 of the superior insert 60091, and the PCD surfaceenhancement 60092 of the inferior insert 60093.

FIGS. 81A and 81B of the spinal implant 600115 shows the PCD surfaceenhancement 60094 of the superior insert 60095, and the PCD surfaceenhancement 60096, 60097, 60098 of the inferior insert 60099.

The spinal implant 600116 shown in FIG. 82A and FIG. 82B depict the PCDsurface enhancement 600100, 600101, 600102 of the superior insert600103, and the PCD surface enhancement 600104, 600105, 600106 of theinferior insert 600107.

The non-congruent spinal implant 600200 FIG. 83A and FIG. 83B depict thediamond enhancement 600108, 600109 of the dome surface 600110 and theconcave running surface 600111. The sides 600112 of the running surface600111 have also been PDC enhanced to prevent metallic wear by contactwith the dome 600110.

FIG. 84 depicts a similar bearing configuration 600201 wherein theconvex running surface 600111 PDC 600109 enhancement does not includethe sides 600116 of the convex running surface 6001111. These implantbearing designs have maximal angular α 600113 and β 600114, andtransitional motion X 600115, but relies totally on the ability of thebearing interface materials to handle the very significant point loadingof the dome 600110 against the concave running surface 600111. Thisbearing, like the bearings 600112 of FIG. 76, benefits greatly from PDCenhancement.

FIG. 85 depicts a congruent spinal disk bearing 600202 with four matingsurfaces which have been PDC enhanced. Two dome surfaces 600117, 600118have PDC surfacing applied, and two concave cup mating receivingsurfaces 600119, 600120 also have PDC surfacing applied.

The spinal implant 203 shown in FIG. 86 has been PDC enhanced on theinferior and superior convex surfaces 600121, 600122 as shown in FIG. 87and FIG. 87-1 to improve the wear resistance and biocompatibility.

FIG. 88 and FIG. 89 depict a spinal disk implant device 600204 that hashad the inferior convex surface 600123 and superior surface 600124enhanced by the application of PDC.

FIG. 90 depicts a congruent spinal disk bearing 600205 with two matingsurfaces which have been PDC enhanced. The inner ball surface 600125 hasPDC surfacing applied, and the outer concave cup mating receivingsurfaces 600126 also have PDC surfacing applied for increased wearresistance and biocompatibility.

The congruent bearing spinal implant shown in FIG. 91 as 600206 has beenPDC enhanced on the inferior dome surface 600127, and the superiorconvex cup surface 600128 to improve the wear resistance andbiocompatibility.

FIG. 92 depicts a congruent spinal disk bearing 600207 with two matingsurfaces which have been PDC enhanced. The inner ball surface 600129 hasPDC surfacing applied, and the outer concave cup mating receivingsurfaces 600130 also have PDC surfacing applied for increased wearresistance and biocompatibility.

Application of Polycrystalline Diamond Compacts for Non-Congruent SpinalImplant Bearing Surfaces

Duplicating the anatomical motion of the human spine using spinal diskreplacement implants is quite challenging. The motions that must bereplicated in the implant device are originally the result of compoundangular and translational motions allowed through the compliance of thepillow-like spine disk. The human vertebral disk has the ability toreshape itself instantaneously predicated on the vector forces appliedto it while at the same time providing a flexible attachment between twoadjacent vertebras. For example, side-to-side bending motion in thecoronal plane causes the spinal disk pad to become thin on the inside ofthe bend angle and larger on the outside of the bend angle. With theangular wedge type reshaping of the spinal disk in the side-to-sidemotion there is also some lateral translation or parallel sliding of thetwo adjacent vertebras. This same motion condition is also exhibitedwith flexion and extension of the body in the sagittal plane; however,the translational motion is significantly greater, often ranging from 1to 2 mm. Lateral rotation in the axial plane does not occur around thecenter of the spinal disk. The actual center of rotation is posterior tothe spinal cord channel, often by several millimeters. This lattermotion is almost completely translational parallel motion with thecommon centers of the adjacent vertebras swinging in an arc.

Spinal disc implants utilizing congruent dome and cup bearings 600208 asin FIG. 93 simply can not adequately duplicate the compound motionsexhibited in the normal human anatomical motion. The very congruency ofthe bearing surfaces makes any kind of translational motion impossible.Lateral rotation FIG. 93-1 in the axial plane angle β 600131, andflexion of FIG. 59 angle θ 5911, and FIG. 60 extension angle φ 5912 inthe sagittal plane are severely restricted. This condition prevents therealization of full anatomical restoration following surgery and tendsto place additional collateral forces on the adjacent spinal disc aboveand below the spinal disk implant leading to possible future problems.

The use of disc implants 600209 employing non-congruent dome and cupbearings of FIGS. 93 and 93-1 can provide substantially superior or nearperfect anatomical duplication. By employing a dome, or similar domeshape, 600132 operating in a convex oval, kidney, or other suitablyshaped mating receiver 600133 both angular and translational motion canbe fully duplicated.

However, non-congruent bearings as utilized in spinal implants tend toproduce overwhelming “point load forces” for typical biocompatiblemetals where the dome contacts the mating convex bearing receiver. These“point load forces” quickly wear away the bearing surfaces generallymaking them inoperable and producing wear particles which react with thesurrounding tissue.

Polycrystalline diamond compact (PDC) utilized in spinal implants withnon-congruent bearing surfaces completely ameliorates the “point loadforces” problem associated with these types of bearings. One embodimentof the devices includes the use of PDC for the convex dome and convexarticulating surface of a non-congruent spinal implant bearing. FIGS. 94and 94-1 depict a non-congruent spinal implant bearing 600209 whereinthe dome 600132 has been fabricated using PDC, and also the convexarticulating surface 600133 has been fabricated using PDC. To accomplishthe necessary compound angular and translational motion required theshape of the dome 600132 would be generally hemispherical but could beelliptical, oval, flattened, or any other configuration that would allowfor the motion required. The convex articulating surface 600133 could beshaped to allow the dome 600132 to not only rock angularly in thedirection desired but to also translate horizontally in the axial planeX 600134.

FIGS. 94 a and 94 a-1 depict an alternative spinal prosthesis 600140 ain which a hemispherical protrusion 600140 a 1 rides along a trough600140 a 1 along an arc of a circle defined by circle center C locatedat the base of the spinal process, and radius R to provide β degrees ofrotational movement within the trough. The trough has a kidney beanappearance.

The actual contour of the convex surface of the recess can be designedto meet any special angular and translational requirement. FIGS. 95,95-1 and 95-2 show a spinal insert 600210 configuration wherein theradius r2 600135 of the convex articulating surface 600138 aresignificantly larger than the dome radius r1 600136 allowing the dome600137 to rotate freely, but to also translate in any direction untilrestrained from further movement by the surrounding tissue.

FIGS. 96, 96-1 and 96-2 depict a modified articulating surfaces 600211wherein the convex articulating surface radius r4 600138 issignificantly larger than the end radiuses r3 600139, and the radius r6600140 is significantly larger than the end radiuses r5 600141. Thecenter radiuses r4 600138 and r6 600140 can be equal, but may also beunequal, also the end radiuses r3 600139 and r5 600141 can be equal, butmay also be unequal. The dome radius r2 600142 would generally beslightly smaller than the smallest of radiuses r3 600139 and r5 600141.

FIGS. 97, 97-1 and 97-2 depict a modified articulating surfaces 600212wherein the recessed articulating surface has a flat area 600143 and endradiuses r3 600144. The end radiuses r3 600144 and r4 600145 can beequal, but may also be unequal. The dome radius r2 600146 wouldgenerally be slightly smaller than the smallest of radiuses r3 600144and r4 600145.

FIGS. 98, 98-1 and 98-2 depict a modified articulating surfaces 600213wherein the convex articulating surface has a conical area 600147defined by the angle φ 600148 and end radiuses r3 600149. The endradiuses r3 600149 and r4 600150 can be equal, but may also be unequal.The dome radius r2 600151 would generally be slightly smaller than thesmallest of radiuses r3 600149 and r4 600150.

FIGS. 99-1 and 49-2 depict a modified articulating surface 600214wherein the convex articulating surface is an elliptically shaped area600152. The elliptical shape 600152 can be equal to the elliptical shape600153, but may also be unequal or another shape configuration. The domeradius r2 600154 would generally be of size to allow for the requiredangular and transitional motion.

FIGS. 100, 100-1 and 100-2 depict a modified articulating surface 600215wherein the convex articulating surface 600155 is a defined by a threedimensional mathematically defined function of the general form:Surface=f(r _(ijk),θ_(ijk),φ_(ijk))

The dome radius r2 600156 would generally be of size to allow for therequired angular and transitional motion.

FIGS. 101 and 101-1 show modified articulating surfaces for a three partspinal implant insert 600216 configuration wherein the radius r1 600157of the convex articulating surface 600158 is significantly larger thanthe dome radiuses r2 600159 allowing the domes to rotate freely, but toalso translate in any direction until restrained from further movementby the surrounding tissue.

FIGS. 102, 102-1 and 102-2 depict modified articulating surfaces for athree part spinal implant 600217 wherein the convex articulating surfaceradiuses r4 600159 is significantly larger than the end radiuses r3600160 and the radius r6 600161 is significantly larger than the endradiuses r5 600162. The center radiuses r4 600159 and r6 600161 can beequal, but may also be unequal, also the end radiuses r3 600160 and r5600162 can be equal, but may also be unequal. The dome radius r2 600163would generally be slightly smaller than the smallest of radiuses r3600160 and r5 600162.

FIGS. 103, 103-1 and 103-2 depict articulating surfaces for a three partspinal implant 600218 wherein the recessed articulating surface has aflat area 600164 and end radiuses r3 600165. The end radiuses r3 600165and r4 600166 can be equal, but may also be unequal. The dome radius r2600167 would generally be slightly smaller than the smallest of radiusesr3 600165 and r4 600166.

FIGS. 104, 104-1 and 104-2 depict an articulating surfaces for a threepart spinal implant 600219 wherein the convex articulating surface has aconical area 600168 defined by the angle φ600169 and end radiuses r3600170. The end radiuses r3 600170 and r4 600171 can be equal, but mayalso be unequal. The dome radius r2 600172 would generally be slightlysmaller than the smallest of radiuses r3 600170 and r4 600171.

FIGS. 105, 105-1 and 105-2 depict an articulating surface for a threepart spinal implant 600220 wherein the convex articulating surface is anelliptically shaped area 600173. The elliptical shape 600173 can beequal to the elliptical shape 600174, but may also be unequal or anothershape configuration. The dome radius r2 600175 would generally be ofsize to allow for the required angular and transitional motion.

FIGS. 106, 106-1 and 106-2 depict articulating surfaces for a three partspinal implant 600221 wherein the convex articulating surface 600176 isa defined by a three dimensional mathematically defined function of thegeneral form:Surface=f(r _(ijk),θ_(ijk),φ_(ijk))

The dome radius r2 600177 would generally be of size to allow for therequired angular and transitional motion.

FIGS. 107 and 107-2 depict a three part spinal implant 600222 whereinthe inferior endplate 600178 and the superior endplate 600179 have beenfabricated using PDC. The outer surfaces 600180, 600181 and theattachment protrusions 600182 which will contact the adjacent vertebraefollowing surgery have been chemically leached using a suitable acidleaching bath such as nitric-hydro sulfuric acid to remove theinterstitial metal between the diamond crystals. The depth of theleached areas 600180, 600181, 600182 would generally range from 0.5 to1.5 mm or more. The voids left between the diamond crystals would beavailable for bone in growth infusion, or the application of other bonegrowth surfaces, or bone growth accelerators such as Hydroxyl Appetite.

FIGS. 108 and 108-1 depict a two part spinal implant 600223 wherein theinferior endplate 600183 and the superior endplate 600184 have beenfabricated using PDC. The outer surfaces 600185, 600186 and theattachment protrusions 600187 which will contact the adjacent vertebraefollowing surgery have been chemically leached using a suitable acidleaching bath such as nitric-hydro sulfuric acid to remove theinterstitial metal between the diamond crystals. The depth of theleached areas 600185, 600186, 600187 would generally range from 0.5 to1.5 mm or more. The voids left between the diamond crystals would beavailable for bone in growth infusion, or the application of other bonegrowth surfaces or bone growth accelerators. In addition, any bonemating surface depicted anywhere herein could include a bone growthaccelerator, a roughened or textured surface to promote bone fixation,pores to permit bone ingrowth, and protrusions to achieve mechanicalbone fixation. In addition, adhesives, glues or epoxies may also be usedto achieve bone fixation.

Spinal Implant Fixation Method Using Screws with Partial HemasphericalEngagement

The devices shown in FIG. 109, 109-1, 109-2, 109-3 a, 109-3 b, 109-4 and109-5 disclose a method and apparatus by which one or more screws 7001may be used to assist in the installation of a spinal implant appliance7002, provide partial fixation during the period of bone in-growth tothe receptor surfaces 7003 of the appliance 7002, and full fixation forthe life of the implant. Another object of this devices is to providefixation without any protrusion of the fixation screws 7001 or othercomponents into the anterior or posterior areas surrounding the spinalimplant device 7002.

Fixation of the spinal implant device 7002 is accomplished by theengagement of slightly less than one-half of the hemispherical portionof the full length of the screw threads 7004 of the fixation screws 7001into the adjacent vertebral bones 7005 as depicted in the Figures. Thecomplementary pressure of the tissue tending to hold and draw the twocorresponding vertebra 7004 together generally provides contactpressures 7006 normal toward the screw thread 7004 surfaces and the bonesurface 7007 allowing adequate frictional and buttressing fixation. Thescrews 7001 are held captive in the appliance 7002 superior 7008 andinferior 7009 plate surfaces 7003 by machining the screw holes 70010slightly below the plate surfaces 7003 of the appliance 7002 whichinterfaces with the bone surfaces 7007. The centerline locatingdimension β 70011 of the screw holes 70010 can be adjusted based on thediameter 70012 of the screw 7001 to ensure that part of the platematerial 70013 extends slightly beyond the centerline of the screw 7001securing it in place within the plates 7008 and 7009. The screw holes70010 in the superior 7008 and the inferior 7009 plates of the implantdevice 7002 can be a drilled hole only 70014 as shown in FIG. 109-3 awith a diameter slightly larger than the major diameter 70012 of thescrews 7001, or tap drilled to the minor of the screw 7001 and thenthreaded 70015 as shown in FIG. 109-3 b.

One, two, or more fixation screws 7001 could be used to provide thedevice 7002 securement. The fixation screws 7001 can also be located atan angel α 70016 ranging between 0.0 Deg and 90 Deg. One embodimentwould locate two screws at an angle α 70016 of approximately 35 Deg.which provides the most favorable strain resistance against componentforces exerted laterally along the horizontal plane of the body. Threadsin the vertebrae 7005 bone surface 7007 can be created by using thescrew 7001 only, or by pre-cutting the threads 70015 using a typicalthread tap of the correct size, form, and length in conjunction with asuitable tap drill hole location fixture and tapping fixture.

The head 70017 of the securing screws 7001 is recessed into a reliefcounter-bore 70018 of FIG. 109-5 to prevent any protrusion at theanterior face of the spinal implant 7002.

The surfaces 7003 of the superior 7008 and inferior 7009 plates of thespinal implant device 2 may be prepared for bone in growth by theapplication of Hydroxy Apatite coating, chemical coating, attached metalbeads, etched surfacing, leached poly crystalline diamond, or any othertreatment that would promote bone ingrowth and attachment.

Spinal Implant Fixation Method Using Screws with Angular Vector BoneEngagement

The devices shown in FIGS. 110, 110-1, 110-2 and 110-3 disclose methodsand apparatuses by which one or more screws 8001 may be used to assistin the installation of a spinal implant appliance 8002, provide partialfixation during the period of bone in-growth to the receptor surfaces8003 of the appliance 8002, and full fixation for the life of theimplant. Another object of this devices is to provide fixation withoutany protrusion of the fixation screws 8001 or other components into theanterior or posterior areas surrounding the spinal implant device 8002.

Fixation of the spinal implant device 8002 is accomplished by theengagement of the screw threads 8004 of the fixation screws 8001 intothe adjacent vertebral bones 8005 as more fully depicted in the Figures.The complementary pressure of the tissue tending to hold and draw thetwo corresponding vertebra 8005 together generally provides contactpressure 8006 toward the bone surfaces 8007 and is augmented bycomponent forces associated with the holding resistance of the screws8001 acting at angles σ 8008 and angle α 8009.

One, two, or more fixation screws 8001 could be used to provide thedevice 8002 securement. The fixation screws 8001 can be located at anangle α 8009 ranging between 0.0 Deg and 90 Deg. and angle σ 8008ranging between approximately 10 Deg. and 45 Deg. One embodiment wouldlocate two screws at an angle σ 8008 of approximately 25 Deg. and angleα 8009 at approximately 35 Deg. which would provide the most favorablestrain resistance against component forces exerted axially along themedian/coronal planes and laterally along the horizontal plane of thebody. Threads in the vertebrae 8005 bone can be created by using thescrew 8001 only, or by pre-cutting the threads 80010 FIG. 110-3 using atypical thread tap of the correct size, form, and length in conjunctionwith a suitable tap drill hole location fixture and tapping fixture.

The head 80011 of the securing screws 8001 is recessed into a reliefcounter-bore 80012 of FIG. 110-3 to prevent any protrusion at theanterior face of the spinal implant 8002.

The surfaces 8003 of the superior 80013 and inferior 80014 plates of thespinal implant device 8002 may be prepared for bone in growth andattachment.

Spinal Implant Fixation Method Using Screws with Angular Vector PlateEngagement

The devices shown in FIGS. 111, 111-1, 111-2 and 111-3 discloses methodsand apparatuses by which one or more screws 8501 may be used to assistin the installation of a spinal implant appliance 8502, provide partialfixation during the period of bone in-growth to the receptor surfaces8503 of the appliance 8502, and full fixation for the life of theimplant. Another object of this devices is to provide fixation withoutany protrusion of the fixation screws 8501 or other components into theanterior or posterior areas surrounding the spinal implant device 8502.

Fixation of the spinal implant device 8502 is accomplished by theengagement of the screw threads 8504 of the fixation screws 8501 intothe superior 8505 and inferior 8506 implant plates 8507 after havingpassed through the adjacent vertebral bones 8508 as more fully depictedin the Figures. The complementary pressure of the tissue tending to holdand draw the two corresponding vertebra 8508 together generally providescontact pressure 8509 toward the bone surfaces 85010 and is augmented bycomponent forces associated with the holding resistance of the screws8501 acting at angles σ 85011 and angle α 85012.

One, two, or more fixation screws 8501 could be used to provide thedevice 8502 securement. The fixation screws 8501 can be located at anangle α 85012 ranging between 0.0 Deg and 90 Deg. and angle car 85011ranging between approximately 10 Deg. and 45 Deg. One embodiment wouldlocate two screws 8501 at an angle σ 85011 of approximately 25 Deg. andangle α 85012 at approximately 35 Deg. which would provide the mostfavorable strain resistance against component forces exerted axiallyalong the median/coronal planes and laterally along the horizontal planeof the body. The fixation screws engage the superior 8505 and inferior8506 plates 8507 at in pre-threaded holes 85013. The fixation screws8501 can be threaded along the full length of the screw 8501, or onlyfor the length which engages the superior 8505 and inferior 8506 plates8507. Clearance holes for the fixation screws 8501 are pre-drilled usinga suitable location fixture to ensure proper location and engagement ofthe screws 8501 into the superior 5850 and inferior 8506 plates 8507.

The head 85014 of the securing screws 8501 is recessed into a reliefcounter-bore 85015 to prevent any protrusion at the anterior face of thespinal implant 8502.

The surfaces 8503 of the superior 8505 and inferior 8506 plates 8507 ofthe spinal implant device 8502 may be prepared for bone in growth.

Spinal Implant Fixation Method Using Securement Lugs with AttachmentScrews and Anti Rotation Positioners

The devices shown in FIGS. 112, 112-1, 112-2 and 112-3 disclose methodand apparatuses by which one or more lugs or clips 9001 may be used toassist in the installation of a spinal implant appliance 9002, providepartial fixation during the period of bone in-growth to the receptorsurfaces 9003 of the appliance 9002, and full fixation for the life ofthe implant. Another object of this device is to provide fixationwithout any protrusion of the fixation clips 9001, screws 9004 or othercomponents into the anterior or posterior areas surrounding the spinalimplant device 9002.

Fixation of the spinal implant device 9002 is accomplished by theengagement of the lugs 9001 into the recesses 9005 previously machinedinto the vertebra by the surgeon. The clips 9001 may be stabilized bythe use of a square or rectangular matching tongue protrusions 9006 andgrooves 9007 running parallel and perpendicular to the median plane ofthe body. Other tongue and groove configurations such as the angulartongue 9008 and angular groove, or a hemispherical tongue and groovescould be used to prevent rotation of the clip.

The head 90012 of the securing screw 9004 is recessed into a reliefcounter-bore 90013 to prevent any protrusion at the anterior face of thespinal implant 9002. The clip 9001 is also rounded 90014 and recessed90015 to prevent any protrusion at the anterior face of the spinalimplant 9002. The surfaces 9003 of the superior 90016 and inferior 90017plates of the spinal implant device 9002 may be prepared for bone ingrowth.

While the present devices and methods have been described andillustrated in conjunction with a number of specific configurations,those skilled in the art will appreciate that variations andmodifications may be made without departing from the principles hereinillustrated, described, and claimed. The present invention, as definedby the appended claims, may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. Theconfigurations described herein are to be considered in all respects asonly illustrative, and not restrictive. All changes which come withinthe meaning and range of equivalency of the claims are to be embracedwithin their scope.

1. An articulating prosthetic spinal implant for implantation betweenvertebrae in a human body, the implant comprising: a first endplatehaving a first side attachable to a spine bone and having a second side,a first body of solid, sintered polycrystalline diamond, said first bodyof diamond being received within a recess on the second side of thefirst endplate, a sintered polycrystalline diamond protrusion on saidfirst body, a protrusion load bearing and articulation surface locatedon said protrusion, said protrusion having a curvature defined by atleast one radius R1, a second endplate having a first side attachable toa spine bone and having a second side, a second body of solid, sinteredpolycrystalline diamond, said second body of diamond being receivedwithin a recess on the second side of the second endplate, a sinteredpolycrystalline diamond receptacle on said second body, a receptacleload bearing and articulation surface located on said receptacle, saidreceptacle having a curvature defined by at least one radius R2, asolvent-catalyst metal located in said sintered polycrystalline diamond,diamond to solvent-catalyst metal bonds between said diamond and saidsolvent-catalyst metal in said sintered polycrystalline diamond, agradient transition zone in said sintered polycrystalline diamond, saidprotrusion and said receptacle being sized and curved to accommodatesaid protrusion protruding into said receptacle, and to accommodate saidprotrusion load bearing and articulation surface contacting saidreceptacle load bearing and articulation surface, said contact of saidprotrusion with said receptacle being accomplished by diamond to diamondcontact of said protrusion and receptacle load bearing and articulationsurfaces, said contact of said protrusion with said receptacle occurringat a diamond to diamond contact point where diamond of said protrusioncontacts diamond of said receptacle, said diamond to diamond contactresulting in diamond on diamond articulation between said protrusion andsaid receptacle, said protrusion being translationally movable withrespect to said receptacle in the axial plan of a human spine, saidtranslational movement being accomplished by a sliding or rollingmovement of diamond against diamond; wherein R1 and R2 are chosen toaccommodate said translational movement; and wherein at least some ofsaid translational movement occurs in the axial plane of a human spineabout an arc of a circle having a radius R3 whose center is located atthe base of the spinal process of a human spine, and wherein R3 is notequal to R1 or R2.
 2. An implant as recited in claim 1 wherein at leasta portion of at least one of said load bearing and articulation surfacesis polished to an Ra value of between about 0.5 to about 0.005 microns.3. An implant as recited in claim 1 further comprising diamond crystalslocated in at least one of said sintered polycrystalline diamondcompacts.
 4. An implant as recited in claim 3 further comprising diamondto diamond chemical bonds between said diamond crystals in said at leastone sintered polycrystalline diamond compact.
 5. An implant as recitedin claim 1 further comprising a crystalline diamond structure located inat least one of said sintered polycrystalline diamond compacts.
 6. Animplant as recited in claim 1 further comprising interstitial spaces insaid crystalline diamond structure of said at least one sinteredpolycrystalline diamond compact.
 7. An implant as recited in claim 6further comprising a solvent-catalyst metal present in at least some ofsaid interstitial spaces of said at least one sintered polycrystallinediamond compact.
 8. An implant as recited in claim 7 wherein anysolvent-catalyst metal has been removed from said interstitial spacesand replaced with another material.
 9. An implant as recited in claim 1wherein at least a portion of at least one of said sinteredpolycrystalline diamond load bearing and articulation surfaces ispolished to an Ra value of between about 0.5 to about 0.005 microns.